Class Illuminate\Support\Composer not found after composer update (Laravel 5.1)

Helo everyone!

So I have a project in Laravel 5.1 and I updated composer, immediately after it was updated I got the following error:

> php artisan clear-compiled


  [ReflectionException]                             
  Class Illuminate\Support\Composer does not exist  


Script php artisan clear-compiled handling the post-update-cmd event returned with error code 1

What I've found on the internet all information available is for Laravel 5.2, mine is Laravel 5.1.

I must mention that all "php artisan" commands do not work, returns same error.

I hope anyone of you knows why this happens and can help me a little bit. Thank you!

via Chebli Mohamed