Hywel is said to have been a son of Rhodri Molwynog and brother of Cynan Dindaethwy ap Rhodri. Cynan and Hywel were recorded as fighting for the control of Anglesey in the early years of the ninth century. Cynan died in 816 and Hywel ruled Gwynedd until his own death.
Some genealogies make Hywel the son of Caradog ap Meirion, and the cousin of Cynan Dindaethwy rather than his brother.
When Hywel died in 825 the direct male line of Cunedda came to an end. He was followed on the throne by Merfyn Frych ap Gwriad - a prince from a cadet branch of Manaw Gododdin - and thus Cunedda's blood was passed on to the new lineage through him and through Ethyllt, the daughter of Cynan Dindaethwy.
J.E. Lloyd (1911) A history of Wales from the earliest times to the Edwardian conquest (Longmam, Green & Co.)