Laravel 5.2, get roles user isn't attached to

I have a pretty basic setup in Laravel with users, role_user and roles. Now, getting roles isn't too hard with return $this->belongsToMany(Role::class, 'role_user');.

But now I want the inverse, the roles the user is NOT attached to. Are there simple Laravel methods to do this, or should I write a query builder for this and if so, how?

via Chebli Mohamed