The Debrune were an ancient offshoot of the Romulans. However, the Romulans are an ancient offshoot of the Vulcans-- this would mean that all 3 alien races have a common ancestor.
In the 4th century, the Debrune had an outpost on the planet Barradas III. (TNG: "Gambit, Part I")
This species was only mentioned in dialogue.