Undefined eager-loaded model in Laravel Echo event - laravel

Question

I'm using Laravel Echo to broadcast events from the server to the client.
The application is a forum, where users can create posts in topics.
Here is the controlled method code where the new post is created, and the event dispatched.
$post = Post::create([
'user_id' => 1,
'topic_id' => request('topic_id'),
'body' => request('body'),
]);
// Fetch the post we've just created, with the relationships this time
$post = Post::with('user', 'topic')->find($post->id);
// Broadcast the event
event(new PostCreated($post));
Here is the event class :
class PostCreated implements ShouldBroadcast
{
public $post;
public function __construct(Post $post)
{
$this->post = $post;
}
public function broadcastOn()
{
return new Channel('topics.' . $this->post->topic_id);
}
}
Finally, here is where the event is intercepted in the front-end :
Echo.channel('topics.' + this.topic.id)
.listen('PostCreated', (e) => {
this.posts.push(e.post);
});
The problem is that I can't seem to access the user property from the listen() method on the front-end.
console.log(e.post.user) // Undefined
If I do a console.log() of the post, I can see the properties of the Post (user_id, topic_id, body, created_at, updated_at) but it's not showing the user or topic properties that were eager-loaded in the controller, before the event was sent.
Those properties are accessible from the event class itself :
// In the __construct() method of the PostCreated event
echo $this->post->user->name; // Works, the name is echo'd
... but somehow are not sent to the front-end when the event is broadcasted.
How can I make sure that the user and topic properties are sent to the client, along with the post itself?