Undefined eager-loaded relationship when using Echo event broadcasting

Question

I am using Laravel Echo in my project to broadcast events to the client-side. Everything is working correctly, however, I am having a problem in eager-loading the relationships of the model for the Event.

My Controller

$chat = new Chat;
$chat->user_id = $request->user_id;
$chat->message = $request->message;
$chat->save();

event( new GetMessages( $chat ));

My Event class:

class GetMessages implements ShouldBroadcast

{
    use Dispatchable, InteractsWithSockets, SerializesModels;

    public $chats;
    public function __construct($chats)
    {
        $this->chats = $chats;
    }

    public function broadcastOn()
    {
        return ['get-messages'];
    }

    public function broadcastAs()
    {
        return 'get-messages';
    }
}

Here is my Laravel Echo

Echo.channel('get-messages')
    .listen('.get-messages', (data) => {
        console.log(data)
    })

Everything is working fine as I expected, except getting the attachments from the Chat.

console.log(data.chats); // Undefined

Is there something I missed? Because as I tested the eager-loaded from the Event class itself, I can access the attachments in there.

public $chats;
public function __construct($chats)
{
    $this->chats = $chats;
    echo $chats->attachments // It's working in here, I can get the attachments
}

Hope I explain it well, Thank you in advance

Cheers!

Here is the console.log

Here is use, it's the default when I created the Event

namespace App\Events;

use Illuminate\Broadcasting\Channel;
use Illuminate\Queue\SerializesModels;
use Illuminate\Broadcasting\PrivateChannel;
use Illuminate\Broadcasting\PresenceChannel;
use Illuminate\Foundation\Events\Dispatchable;
use Illuminate\Broadcasting\InteractsWithSockets;
use Illuminate\Contracts\Broadcasting\ShouldBroadcast;

class GetMessages implements ShouldBroadcast
{
    use Dispatchable, InteractsWithSockets, SerializesModels;
...