Brycheiniog

A kingdom in Wales during the medieval times, founded by the early King Brychan Brycheiniog. The throne seat of Brycheiniog was in Talgarth in the Black Mountains of the lands of Garth Madrun. 
The kingdom of Brycheiniog was settled by Irish raiders in the early-5th century, of the Uí Liatháin and the Deisi, whose power had grown great in Wales until they were reduced by the sons of Cunedda. It was reconstituted by, and named after, the Hiberno-Welsh prince named Brychan out of the old Welsh kingdom of Garth Madrun, centered in Talgarth in the mid-5th century. Brychan was a son of Anlach, an Irish settler who had peacefully taken control of the area by marrying Marchel, the heiress of Garth Madrun to his son. Brychan fathered an extremely large number of children, and his eldest son, Rhain Dremrudd (Rhain the red-faced), founded a dynasty which ruled the kingdom uninterrupted until the mid 7th century; his successors were: Rhigeneu ap Rhain, Llywarch ap Rhygeneu, Idwallon ap Llywarch, Rhiwallon ap Idwallon. 
Brycheiniog belonged to the Demetae in pre-Roman times. 
Also: Teyrnas Brycheiniog, or previously Garth Madrun