...Traditionally, Brychen himself was born in Ireland, the son of a minor tribal king named Anlach, and moved with his parents to Wales. This ties in with the settling of the Irish Déisi in south-west Wales who took over command of the British territory of Demetia, although Anlach's pedigree would suggest that he was already in Wales, given that his grandfather had been the son of the leader of the Déisi exodus from Ireland. Instead, Anlach's own 'moving to Wales' should perhaps be seen more in the context of his recent ancestors having moved there and his own grandfather having migrated further east into Garthmadrun (although see an alternative at circa 450, below). When Brychen was made king upon the death of his father, the area of Garthmadrun (or Garth Madrun, both older spellings of the modern Garth Madryn) was renamed Brycheiniog in his honour. This suggests that Anlach himself was not the territory's king. Instead he was probably a sub-king, governing Garthmadrun for the core Déisi to the west....
c. 420 Anlach marries Marchel, whom Celtic works describe as the 'heiress of Garthmadrun'. The same works give Anlach's father as Cornac or Coronac, who is generally linked to Cormac mac Urb of the Déisi. Given the calculation that the Déisi had arrived in Dyfed around AD 300, this would give them ample time to become integrated into the regional nobility and for their leading sons to marry the offspring of the surviving Brito-Welsh nobility, hence Anlach's marriage to Marchel.
c. 450 Anlach has probably not been a king in his own right in Garthmadrun, but a sub-king or regional governor for the core Déisi to the west. His death means that he is succeeded by his son, Brychen, and it is now that the territory seemingly becomes an independent kingdom. Garthmadrun is renamed Brycheiniog to show that it is now firmly the land of Brychen and his followers. 1