In the TV series Entourage, we know that Vince & Johnny Drama are half brothers, but it is not clear that whether they have same mother or same father.
According to Wikipedia there are certain instances in the TV show which indicate that the exact relation between Vince & Drama is not clear, for example - Vince and Drama share the same last name.
They appear to have the same mother in the episode "Aquamom" when Johnny calls himself her "first born". However, Drama calls Vincent's mother "your mom" in the episode "My Maserati Does 185".
I guess the fans know more details and we can have more inputs on this topic to determine how Vince and Drama are actually related. How are Vince and Drama exactly related?