diff --git a/lib/shared/messages/create-sidebar-message-spec.js b/lib/shared/messages/create-sidebar-message-spec.js
--- a/lib/shared/messages/create-sidebar-message-spec.js
+++ b/lib/shared/messages/create-sidebar-message-spec.js
@@ -6,6 +6,7 @@
   pushTypes,
   type CreateMessageInfoParams,
   type MessageSpec,
+  type NotificationTextsParams,
 } from './message-spec.js';
 import { joinResult } from './utils.js';
 import type { PlatformDetails } from '../../types/device-types.js';
@@ -28,6 +29,7 @@
   type EntityText,
   pluralizeEntityText,
 } from '../../utils/entity-text.js';
+import { isMentioned } from '../mention-utils.js';
 import { hasMinCodeVersion } from '../version-utils.js';
 
 export const createSidebarMessageSpec: MessageSpec<
@@ -178,6 +180,7 @@
   async notificationTexts(
     messageInfos: $ReadOnlyArray<MessageInfo>,
     threadInfo: ThreadInfo,
+    params: NotificationTextsParams,
   ): Promise<NotifTexts> {
     const firstMessageInfo = messageInfos[0];
     invariant(
@@ -196,7 +199,19 @@
 
     let body = `started a thread in response to `;
     body = ET`${body} ${sourceMessageAuthorPossessive} message`;
-    if (initialName) {
+
+    const { username } = params.notifTargetUserInfo;
+
+    const secondMessageInfo = messageInfos[1];
+    if (
+      username &&
+      secondMessageInfo &&
+      secondMessageInfo.type === messageTypes.SIDEBAR_SOURCE &&
+      secondMessageInfo.sourceMessage.type === messageTypes.TEXT &&
+      isMentioned(username, secondMessageInfo.sourceMessage.text)
+    ) {
+      body = ET`${body} that tagged you`;
+    } else if (initialName) {
       body = ET`${body} "${initialName}"`;
     }