diff --git a/packages/discord.js/src/structures/PartialGroupDMChannel.js b/packages/discord.js/src/structures/PartialGroupDMChannel.js
index 935ca5f5c65cf..0e2bff1244f66 100644
--- a/packages/discord.js/src/structures/PartialGroupDMChannel.js
+++ b/packages/discord.js/src/structures/PartialGroupDMChannel.js
@@ -1,12 +1,14 @@
 'use strict';
 
 const { BaseChannel } = require('./BaseChannel');
+const TextBasedChannel = require('./interfaces/TextBasedChannel');
 const { DiscordjsError, ErrorCodes } = require('../errors');
 const PartialGroupDMMessageManager = require('../managers/PartialGroupDMMessageManager');
 
 /**
  * Represents a Partial Group DM Channel on Discord.
  * @extends {BaseChannel}
+ * @implements {TextBasedChannel}
  */
 class PartialGroupDMChannel extends BaseChannel {
   constructor(client, data) {
@@ -70,21 +72,12 @@ class PartialGroupDMChannel extends BaseChannel {
        * The timestamp when the last pinned message was pinned, if there was one
        * @type {?number}
        */
-      this.lastPinTimestamp = data.last_pin_timestamp;
+      this.lastPinTimestamp = Date.parse(data.last_pin_timestamp);
     } else {
       this.lastPinTimestamp ??= null;
     }
   }
 
-  /**
-   * The date when the last pinned message was pinned, if there was one
-   * @type {?Date}
-   * @readonly
-   */
-  get lastPinAt() {
-    return this.lastPinTimestamp && new Date(this.lastPinTimestamp);
-  }
-
   /**
    * The URL to this channel's icon.
    * @param {ImageURLOptions} [options={}] Options for the image URL
@@ -114,6 +107,25 @@ class PartialGroupDMChannel extends BaseChannel {
   fetch() {
     return Promise.reject(new DiscordjsError(ErrorCodes.FetchGroupDMChannel));
   }
+
+  // These are here only for documentation purposes - they are implemented by TextBasedChannel
+  /* eslint-disable no-empty-function */
+  get lastMessage() {}
+  get lastPinAt() {}
+  createMessageComponentCollector() {}
+  awaitMessageComponent() {}
 }
 
+TextBasedChannel.applyToClass(PartialGroupDMChannel, true, [
+  'bulkDelete',
+  'send',
+  'sendTyping',
+  'createMessageCollector',
+  'awaitMessages',
+  'fetchWebhooks',
+  'createWebhook',
+  'setRateLimitPerUser',
+  'setNSFW',
+]);
+
 module.exports = PartialGroupDMChannel;
diff --git a/packages/discord.js/typings/index.d.ts b/packages/discord.js/typings/index.d.ts
index 88151c04daece..f5b685805041f 100644
--- a/packages/discord.js/typings/index.d.ts
+++ b/packages/discord.js/typings/index.d.ts
@@ -1334,7 +1334,7 @@ export interface ResolvedFile {
 // tslint:disable-next-line no-empty-interface
 export interface DMChannel
   extends Omit<
-    TextBasedChannelFields<false>,
+    TextBasedChannelFields<false, true>,
     'bulkDelete' | 'fetchWebhooks' | 'createWebhook' | 'setRateLimitPerUser' | 'setNSFW'
   > {}
 export class DMChannel extends BaseChannel {
@@ -2582,6 +2582,19 @@ export class OAuth2Guild extends BaseGuild {
   public permissions: Readonly<PermissionsBitField>;
 }
 
+export interface PartialGroupDMChannel
+  extends Omit<
+    TextBasedChannelFields<false, false>,
+    | 'bulkDelete'
+    | 'send'
+    | 'sendTyping'
+    | 'createMessageCollector'
+    | 'awaitMessages'
+    | 'fetchWebhooks'
+    | 'createWebhook'
+    | 'setRateLimitPerUser'
+    | 'setNSFW'
+  > {}
 export class PartialGroupDMChannel extends BaseChannel {
   private constructor(client: Client<true>, data: RawPartialGroupDMChannelData);
   public type: ChannelType.GroupDM;
@@ -2589,11 +2602,7 @@ export class PartialGroupDMChannel extends BaseChannel {
   public name: string | null;
   public icon: string | null;
   public recipients: PartialRecipient[];
-  public messages: PartialGroupDMMessageManager;
   public ownerId: Snowflake | null;
-  public lastMessageId: Snowflake | null;
-  public lastPinTimestamp: number | null;
-  get lastPinAt(): Date | null;
   public iconURL(options?: ImageURLOptions): string | null;
   public fetchOwner(options?: BaseFetchOptions): Promise<User>;
   public toString(): ChannelMention;
@@ -4722,13 +4731,13 @@ export interface PartialTextBasedChannelFields<InGuild extends boolean = boolean
   send(options: string | MessagePayload | MessageCreateOptions): Promise<Message<InGuild>>;
 }
 
-export interface TextBasedChannelFields<InGuild extends boolean = boolean>
+export interface TextBasedChannelFields<InGuild extends boolean = boolean, InDM extends boolean = boolean>
   extends PartialTextBasedChannelFields<InGuild> {
   lastMessageId: Snowflake | null;
   get lastMessage(): Message | null;
   lastPinTimestamp: number | null;
   get lastPinAt(): Date | null;
-  messages: If<InGuild, GuildMessageManager, DMMessageManager>;
+  messages: If<InGuild, GuildMessageManager, If<InDM, DMMessageManager, PartialGroupDMMessageManager>>;
   awaitMessageComponent<ComponentType extends MessageComponentType>(
     options?: AwaitMessageCollectorOptionsParams<ComponentType, true>,
   ): Promise<MappedInteractionTypes[ComponentType]>;