diff --git a/html/semantics/popovers/idlharness.tentative.html b/html/semantics/popovers/idlharness.tentative.html
index 478dec84c8195ff..d1a258bb4ad3ac3 100644
--- a/html/semantics/popovers/idlharness.tentative.html
+++ b/html/semantics/popovers/idlharness.tentative.html
@@ -41,9 +41,12 @@
         'document.getElementById("b3")',
       ],
       BeforeToggleEvent: [
-        'new BeforeToggleEvent("beforetoggle")',
-        'new BeforeToggleEvent("beforetoggle", {currentState: "open"})',
-        'new BeforeToggleEvent("beforetoggle", {currentState: "open",newState: "open"})',
+        'new PopoverToggleEvent("beforetoggle")',
+        'new PopoverToggleEvent("beforetoggle", {currentState: "open"})',
+        'new PopoverToggleEvent("beforetoggle", {currentState: "open",newState: "open"})',
+        'new PopoverToggleEvent("aftertoggle")',
+        'new PopoverToggleEvent("aftertoggle", {currentState: "open"})',
+        'new PopoverToggleEvent("aftertoggle", {currentState: "open",newState: "open"})',
       ],
     });
   }
diff --git a/html/semantics/popovers/popover-events.tentative.html b/html/semantics/popovers/popover-events.tentative.html
index c88dc21dfa23fba..b96a0f5a53f489d 100644
--- a/html/semantics/popovers/popover-events.tentative.html
+++ b/html/semantics/popovers/popover-events.tentative.html
@@ -16,19 +16,40 @@
       const popover = document.querySelector('[popover]');
       assert_false(popover.matches(':open'));
       let showCount = 0;
+      let afterShowCount = 0;
       let hideCount = 0;
+      let afterHideCount = 0;
       function listener(e) {
-        if (e.newState === "open") {
-          assert_equals(e.currentState,"closed",'Popover toggleevent states should be "open" and "closed"')
-          assert_true(e.target.matches(':closed'),'The popover should be in the :closed state when the opening event fires.');
-          assert_false(e.target.matches(':open'),'The popover should *not* be in the :open state when the opening event fires.');
-          ++showCount;
+        if (e.type === "beforetoggle") {
+          if (e.newState === "open") {
+            assert_equals(e.currentState,"closed",'The "beforetoggle" event should be fired before the popover is open');
+            assert_true(e.target.matches(':closed'),'The popover should be in the :closed state when the opening event fires.');
+            assert_false(e.target.matches(':open'),'The popover should *not* be in the :open state when the opening event fires.');
+            ++showCount;
+          } else {
+            assert_equals(e.newState,"closed",'Popover toggleevent states should be "open" and "closed"');
+            assert_equals(e.currentState,"open",'The "beforetoggle" event should be fired before the popover is closed')
+            assert_true(e.target.matches(':open'),'The popover should be in the :open state when the hiding event fires.');
+            assert_false(e.target.matches(':closed'),'The popover should *not* be in the :closed state when the hiding event fires.');
+            ++hideCount;
+          }
         } else {
-          assert_equals(e.currentState,"open",'Popover toggleevent states should be "open" and "closed"')
-          assert_equals(e.newState,"closed",'Popover toggleevent states should be "open" and "closed"')
-          assert_true(e.target.matches(':open'),'The popover should be in the :open state when the hiding event fires.');
-          assert_false(e.target.matches(':closed'),'The popover should *not* be in the :closed state when the hiding event fires.');
-          ++hideCount;
+          assert_equals(e.type,"aftertoggle",'Popover events should be "beforetoggle" and "aftertoggle"')
+          if (e.newState === "open") {
+            assert_equals(e.currentState,"open",'Aftertoggle should be fired after the popover is open');
+            if (document.body.contains(e.target)) {
+              assert_true(e.target.matches(':open'),'The popover should be in the :open state when the after opening event fires.');
+              assert_false(e.target.matches(':closed'),'The popover should *not* be in the :closed state when the after opening event fires.');
+            }
+            ++afterShowCount;
+          } else {
+            assert_equals(e.newState,"closed",'Popover toggleevent states should be "open" and "closed"');
+            assert_equals(e.currentState,"closed",'Aftertoggle should be fired after the popover is closed');
+            assert_true(e.target.matches(':closed'),'The popover should be in the :closed state when the after hiding event fires.');
+            assert_false(e.target.matches(':open'),'The popover should *not* be in the :open state when the after hiding event fires.');
+            ++afterHideCount;
+          }
+          e.preventDefault(); // "aftertoggle" should not be cancelable.
         }
       };
       switch (method) {
@@ -36,34 +57,52 @@
           const controller = new AbortController();
           const signal = controller.signal;
           t.add_cleanup(() => controller.abort());
-          // The 'beforetoggle' event bubbles.
+          // These events bubble.
           document.addEventListener('beforetoggle', listener, {signal});
+          document.addEventListener('aftertoggle', listener, {signal});
           break;
         case "attribute":
           assert_false(popover.hasAttribute('onbeforetoggle'));
           t.add_cleanup(() => popover.removeAttribute('onbeforetoggle'));
           popover.onbeforetoggle = listener;
+          assert_false(popover.hasAttribute('onaftertoggle'));
+          t.add_cleanup(() => popover.removeAttribute('onaftertoggle'));
+          popover.onaftertoggle = listener;
           break;
         default: assert_unreached();
       }
       assert_equals(0,showCount);
       assert_equals(0,hideCount);
+      assert_equals(0,afterShowCount);
+      assert_equals(0,afterHideCount);
       popover.showPopover();
       assert_true(popover.matches(':open'));
       assert_equals(1,showCount);
       assert_equals(0,hideCount);
+      assert_equals(0,afterShowCount);
+      assert_equals(0,afterHideCount);
       await waitForRender();
+      assert_equals(1,afterShowCount,'aftertoggle show is fired asynchronously');
+      assert_equals(0,afterHideCount);
       assert_true(popover.matches(':open'));
       popover.hidePopover();
       assert_false(popover.matches(':open'));
       assert_equals(1,showCount);
       assert_equals(1,hideCount);
+      assert_equals(1,afterShowCount);
+      assert_equals(0,afterHideCount);
+      await waitForRender();
+      assert_equals(1,afterShowCount);
+      assert_equals(1,afterHideCount,'aftertoggle hide is fired asynchronously');
+      // No additional events
+      await waitForRender();
       await waitForRender();
-      // No additional events after animation frame
       assert_false(popover.matches(':open'));
       assert_equals(1,showCount);
       assert_equals(1,hideCount);
-    }, `Beforetoggle event (${method}) get properly dispatched for popovers`);
+      assert_equals(1,afterShowCount);
+      assert_equals(1,afterHideCount);
+    }, `The "beforetoggle" event (${method}) get properly dispatched for popovers`);
   }
 
   promise_test(async t => {
@@ -86,7 +125,7 @@
     assert_true(popover.matches(':open'));
     popover.hidePopover();
     assert_false(popover.matches(':open'));
-  }, 'Beforetoggle event is cancelable for the "opening" transition');
+  }, 'The "beforetoggle" event is cancelable for the "opening" transition');
 
   promise_test(async t => {
     const popover = document.querySelector('[popover]');
@@ -104,6 +143,6 @@
     await waitForRender(); // Check for async events also
     await waitForRender(); // Check for async events also
     assert_false(popover.matches(':open'));
-  }, 'Beforetoggle event is not fired for element removal');
+  }, 'The "beforetoggle" event is not fired for element removal');
 };
 </script>
diff --git a/html/semantics/popovers/toggleevent-interface.tentative.html b/html/semantics/popovers/toggleevent-interface.tentative.html
index 8ee63c4071856c0..4d437b0c0ad523c 100644
--- a/html/semantics/popovers/toggleevent-interface.tentative.html
+++ b/html/semantics/popovers/toggleevent-interface.tentative.html
@@ -7,200 +7,200 @@
 
 <script>
 test(function() {
-  var event = new BeforeToggleEvent("");
-  assert_true(event instanceof window.BeforeToggleEvent);
-}, "the event is an instance of BeforeToggleEvent");
+  var event = new PopoverToggleEvent("");
+  assert_true(event instanceof window.PopoverToggleEvent);
+}, "the event is an instance of PopoverToggleEvent");
 
 test(function() {
-  var event = new BeforeToggleEvent("");
+  var event = new PopoverToggleEvent("");
   assert_true(event instanceof window.Event);
 }, "the event inherts from Event");
 
 test(function() {
   assert_throws_js(TypeError, function() {
-    new BeforeToggleEvent();
+    new PopoverToggleEvent();
   }, 'First argument (type) is required, so was expecting a TypeError.');
 }, 'Missing type argument');
 
 test(function() {
-  var event = new BeforeToggleEvent("test");
+  var event = new PopoverToggleEvent("test");
   assert_equals(event.type, "test");
 }, "type argument is string");
 
 test(function() {
-  var event = new BeforeToggleEvent(null);
+  var event = new PopoverToggleEvent(null);
   assert_equals(event.type, "null");
 }, "type argument is null");
 
 test(function() {
-  var event = new BeforeToggleEvent(undefined);
+  var event = new PopoverToggleEvent(undefined);
   assert_equals(event.type, "undefined");
 }, "event type set to undefined");
 
 test(function() {
-  var event = new BeforeToggleEvent("test");
+  var event = new PopoverToggleEvent("test");
   assert_equals(event.currentState, "");
 }, "currentState has default value of empty string");
 
 test(function() {
-  var event = new BeforeToggleEvent("test");
+  var event = new PopoverToggleEvent("test");
   assert_readonly(event, "currentState", "readonly attribute value");
 }, "currentState is readonly");
 
 test(function() {
-  var event = new BeforeToggleEvent("test");
+  var event = new PopoverToggleEvent("test");
   assert_equals(event.newState, "");
 }, "newState has default value of empty string");
 
 test(function() {
-  var event = new BeforeToggleEvent("test");
+  var event = new PopoverToggleEvent("test");
   assert_readonly(event, "newState", "readonly attribute value");
 }, "newState is readonly");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", null);
+  var event = new PopoverToggleEvent("test", null);
   assert_equals(event.currentState, "");
   assert_equals(event.newState, "");
-}, "BeforeToggleEventInit argument is null");
+}, "PopoverToggleEventInit argument is null");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", undefined);
+  var event = new PopoverToggleEvent("test", undefined);
   assert_equals(event.currentState, "");
   assert_equals(event.newState, "");
-}, "BeforeToggleEventInit argument is undefined");
+}, "PopoverToggleEventInit argument is undefined");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {});
+  var event = new PopoverToggleEvent("test", {});
   assert_equals(event.currentState, "");
   assert_equals(event.newState, "");
-}, "BeforeToggleEventInit argument is empty dictionary");
+}, "PopoverToggleEventInit argument is empty dictionary");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: "sample"});
+  var event = new PopoverToggleEvent("test", {currentState: "sample"});
   assert_equals(event.currentState, "sample");
 }, "currentState set to 'sample'");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: undefined});
+  var event = new PopoverToggleEvent("test", {currentState: undefined});
   assert_equals(event.currentState, "");
 }, "currentState set to undefined");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: null});
+  var event = new PopoverToggleEvent("test", {currentState: null});
   assert_equals(event.currentState, "null");
 }, "currentState set to null");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: false});
+  var event = new PopoverToggleEvent("test", {currentState: false});
   assert_equals(event.currentState, "false");
 }, "currentState set to false");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: true});
+  var event = new PopoverToggleEvent("test", {currentState: true});
   assert_equals(event.currentState, "true");
 }, "currentState set to true");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: 0.5});
+  var event = new PopoverToggleEvent("test", {currentState: 0.5});
   assert_equals(event.currentState, "0.5");
 }, "currentState set to a number");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: []});
+  var event = new PopoverToggleEvent("test", {currentState: []});
   assert_equals(event.currentState, "");
 }, "currentState set to []");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: [1, 2, 3]});
+  var event = new PopoverToggleEvent("test", {currentState: [1, 2, 3]});
   assert_equals(event.currentState, "1,2,3");
 }, "currentState set to [1, 2, 3]");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {currentState: {sample: 0.5}});
+  var event = new PopoverToggleEvent("test", {currentState: {sample: 0.5}});
   assert_equals(event.currentState, "[object Object]");
 }, "currentState set to an object");
 
 test(function() {
-  var event = new BeforeToggleEvent("test",
+  var event = new PopoverToggleEvent("test",
       {currentState: {valueOf: function () { return 'sample'; }}});
   assert_equals(event.currentState, "[object Object]");
 }, "currentState set to an object with a valueOf function");
 
 test(function() {
   var eventInit = {currentState: "sample",newState: "sample2"};
-  var event = new BeforeToggleEvent("test", eventInit);
+  var event = new PopoverToggleEvent("test", eventInit);
   assert_equals(event.currentState, "sample");
   assert_equals(event.newState, "sample2");
-}, "BeforeToggleEventInit properties set value");
+}, "PopoverToggleEventInit properties set value");
 
 test(function() {
   var eventInit = {currentState: "open",newState: "closed"};
-  var event = new BeforeToggleEvent("beforetoggle", eventInit);
+  var event = new PopoverToggleEvent("beforetoggle", eventInit);
   assert_equals(event.currentState, "open");
   assert_equals(event.newState, "closed");
-}, "BeforeToggleEventInit properties set value 2");
+}, "PopoverToggleEventInit properties set value 2");
 
 test(function() {
   var eventInit = {currentState: "closed",newState: "open"};
-  var event = new BeforeToggleEvent("beforetoggle", eventInit);
+  var event = new PopoverToggleEvent("aftertoggle", eventInit);
   assert_equals(event.currentState, "closed");
   assert_equals(event.newState, "open");
-}, "BeforeToggleEventInit properties set value 3");
+}, "PopoverToggleEventInit properties set value 3");
 
 test(function() {
   var eventInit = {currentState: "open",newState: "open"};
-  var event = new BeforeToggleEvent("beforetoggle", eventInit);
+  var event = new PopoverToggleEvent("beforetoggle", eventInit);
   assert_equals(event.currentState, "open");
   assert_equals(event.newState, "open");
-}, "BeforeToggleEventInit properties set value 4");
+}, "PopoverToggleEventInit properties set value 4");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: "sample"});
+  var event = new PopoverToggleEvent("test", {newState: "sample"});
   assert_equals(event.newState, "sample");
 }, "newState set to 'sample'");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: undefined});
+  var event = new PopoverToggleEvent("test", {newState: undefined});
   assert_equals(event.newState, "");
 }, "newState set to undefined");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: null});
+  var event = new PopoverToggleEvent("test", {newState: null});
   assert_equals(event.newState, "null");
 }, "newState set to null");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: false});
+  var event = new PopoverToggleEvent("test", {newState: false});
   assert_equals(event.newState, "false");
 }, "newState set to false");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: true});
+  var event = new PopoverToggleEvent("test", {newState: true});
   assert_equals(event.newState, "true");
 }, "newState set to true");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: 0.5});
+  var event = new PopoverToggleEvent("test", {newState: 0.5});
   assert_equals(event.newState, "0.5");
 }, "newState set to a number");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: []});
+  var event = new PopoverToggleEvent("test", {newState: []});
   assert_equals(event.newState, "");
 }, "newState set to []");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: [1, 2, 3]});
+  var event = new PopoverToggleEvent("test", {newState: [1, 2, 3]});
   assert_equals(event.newState, "1,2,3");
 }, "newState set to [1, 2, 3]");
 
 test(function() {
-  var event = new BeforeToggleEvent("test", {newState: {sample: 0.5}});
+  var event = new PopoverToggleEvent("test", {newState: {sample: 0.5}});
   assert_equals(event.newState, "[object Object]");
 }, "newState set to an object");
 
 test(function() {
-  var event = new BeforeToggleEvent("test",
+  var event = new PopoverToggleEvent("test",
       {newState: {valueOf: function () { return 'sample'; }}});
   assert_equals(event.newState, "[object Object]");
 }, "newState set to an object with a valueOf function");
diff --git a/interfaces/popover.tentative.idl b/interfaces/popover.tentative.idl
index 7e38b1f09ac9a5e..bf23c7641d94e80 100644
--- a/interfaces/popover.tentative.idl
+++ b/interfaces/popover.tentative.idl
@@ -13,13 +13,13 @@ interface mixin PopoverTargetElement {
 HTMLInputElement includes PopoverTargetElement;
 HTMLButtonElement includes PopoverTargetElement;
 
-interface BeforeToggleEvent : Event {
-    constructor(DOMString type, optional BeforeToggleEventInit eventInitDict = {});
+interface PopoverToggleEvent : Event {
+    constructor(DOMString type, optional PopoverToggleEventInit eventInitDict = {});
     readonly attribute DOMString currentState;
     readonly attribute DOMString newState;
 };
 
-dictionary BeforeToggleEventInit : EventInit {
+dictionary PopoverToggleEventInit : EventInit {
     DOMString currentState = "";
     DOMString newState = "";
 };