Concatenate BelongsTo Relationships With Eloquent

I have a Class (and DB table) Invoices that belongs to Subcat2 (a Subcat2 item has many invoices), and the Subcat2 belongs to Subcat1 (a Subcat1 has many subcat2s).

Now I'm retrieving information from the Invoices class with subcat2 as well:

$invoices = Invoice::with('subcat2')->get();

what if i need to join together also subcat1 using the Subcat2-Subcat1 relationship?

You need use Nested Eager Loading according to Laravel Documentation:

$invoices = Invoice::with('subcat2.subcat1')->get();