diff --git a/src/models/event-timeline-set.js b/src/models/event-timeline-set.js
index <HASH>..<HASH> 100644
--- a/src/models/event-timeline-set.js
+++ b/src/models/event-timeline-set.js
@@ -746,6 +746,10 @@ EventTimelineSet.prototype._aggregateRelations = function(event) {
             eventType,
             this.room,
         );
+        const relatesToEvent = this.findEventById(relatesToEventId);
+        if (relatesToEvent) {
+            relatesToEvent.emit("Event.relationsCreated", relationType, eventType);
+        }
     }
 
     relationsWithEventType.addEvent(event);
Add `Event.relationsCreated` event to listen for future relations collections

If you ask for relations but none currently exist, we return `null` to avoid the
overhead of many empty relations objects in memory. However, we still want some
way to alert consumers when one _is_ later made, so this event level event
provides that.

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