Powys Wenwynwwyn or Powys Cyfeiliog was the southern portion of the former princely state of Powys which split following the death of Madog ap Maredudd of Powys in 1160. The realm had been split, with the northern portion (Maelor) going to Gruffydd Maelor I and becoming known, eventually, as Powys Fadog and the southern portion (Cyfeiliog) going to Owain Cyfeiliog and becoming known, eventually, as Powys Wenwynwyn after Prince Gwenwynwyn ab Owain, its second ruler.
Powys Wenwynwyn and Gwynedd became bitter rivals in the years that followed with the former frequently allying itself with England to further its own aims in weakening the latter.
Princes of Powys Wenwynwyn
- 1160–1195 Owain Cyfeiliog married dau. of Owain Gwynedd and abdicated in 1195
- 1195–1216 Gwenwynwyn ab Owain
Gwenwynwyn seized Arwystli in 1197 when he was aligned with England. Following the marriage of Llywelyn the Great and Joan of England in 1208, warfare broke out once more between Gwenwynwyn and Llywelyn. In 1212 Gwenwynwyn's ancient royal seat at Mathrafal was destroyed and he was evicted from his territories. He changed allegiances again and was restored to his realm in 1215 making a new capital at Welshpool. In 1216 he was defeated in battle with the forces of Llywelyn and fled to England, where he died shortly afterwards. He was succeeded by his son.
- 1216–1286 Gruffydd ap Gwenwynwyn (alias Griffith de la Pole)
Gruffydd ap Gwenwynwyn was forced to submit to Llywelyn Fawr in 1216. Like his father he repeatedly switched allegiances and was invested with the lordships of Arwystli, Cyfeiliog, Mawddwy, Caereinion, Y Tair Swydd and Upper Mochnant by Henry III of England in 1241.
Gruffydd ap Gwenwynwyn married Hawise daughter of John Le Strange of Salop in 1241. He appears to have changed the family name around this time to de la Pole, perhaps to reflect the new political certainties.
He transferred his allegiance back to Llywelyn ap Gruffydd in 1263 before returning to England's protection again after 1277 where he plotted the murder of Prince Llywelyn with his rival's own brother, Dafydd ap Gruffydd. His forces mobilised during the Welsh War of 1282–1283 with those of John Le Strange and Hugh le Despenser.
It was their soldiers who ambushed and killed the last native Prince of Wales near Builth on that fateful day in 1282.
After the Statute of Rhuddlan in 1284 all of the old princely titles in Wales ceased to exist. The realm of Powys Wenwynwyn became, almost entirely, the traditional county of Montgomeryshire. The ruling family of Powys did survive in the children and future descendants of Gruffydd ap Gwenwynwyn, henceforth known as the De La Pole Family. Their descendants went on to play a major role in England as Earls of Suffolk. Gruffydd died in 1286 and was succeeded by his son Owain who was in turn succeeded by his eldest son William.
- 1286–1293 Owen de la Pole (ap Gruffydd)
- 1293–1329 Sir William de la Pole (the elder)
- 1329–1366 Sir William de la Pole (the younger)
- 1366–1389 Lord Michael de la Pole, 1st Earl of Suffolk
- 1389–1415 Lord Michael de la Pole, 2nd Earl of Suffolk
- 1415 Lord Michael de la Pole, 3rd Earl of Suffolk
- 1415–1450 Lord William de la Pole, 1st Duke of Suffolk
- 1450–1491 Lord John de la Pole, 2nd Duke of Suffolk
- 1491–1513 Lord Edmund de la Pole, 3rd Duke of Suffolk
- 1513–1525 Richard de la Pole
When Richard de la Pole was killed in exile at the Battle of Pavia the line of Gruffydd ap Gwenwynwyn is thought to have become extinct with the known descendants of all male heirs of his house being expired.