Llywelyn ap Seisyll

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Llywelyn ap Seisyll (or Seisyllt; died 1023) was an 11th-century king of Gwynedd and Deheubarth in present-day Wales. He was noted as "King of the Britons" in the Irish Annals of Ulster.


Little is known about Llywelyn's father Seisyll, who may not have been of royal blood. According to some genealogies, Seisyll and his son were associated with Rhuddlan, perhaps as lords of its commote in Rhos. Llywelyn's wife Angharad was the daughter of Maredudd, a grandson of Hywel Dda's southern dynasty who ruled much of Wales from AD 989 to 999.


Llywelyn won control of Gwynedd in 1018 when he defeated the usurper Aeddan in battle, killing him and his four sons. He gained control of Dyfed in 1022 after defeating Rhain – the Irish pretender who ruled there under the pretense of being Maredudd's son – in the Battle of Abergwili.

According to the Brut y Tywysogion, Llywelyn's reign was one of prosperity: "There was no one needy in his realm, and there was no town empty or deserted". He died prematurely in 1023. His son Gruffydd, though still a youth when his father died, was later able to gain control of almost the whole of Wales.


Regnal titles
Preceded by
Aeddan ap Blegywryd
King of Gwynedd
Succeeded by
Iago ab Idwal ap Meurig
Preceded by
Cadell ab Einion
King of Deheubarth
Succeeded by
Rhydderch ap Iestyn