Dictionary of National Biography, 1885-1900/Rhiwallon ap Cynfyn
RHIWALLON ap CYNFYN (d. 1069), Welsh prince, was the son of Cynfyn ap Gwerstan, and on the downfall of Gruffydd ap Llywelyn in 1063 received (with his brother Bleddyn) North Wales on condition of faithfully serving Edward the Confessor ‘everywhere by water and by land.’ As the son of Angharad, daughter of Maredudd ab Owain ap Hywel Dda, he was Gruffydd's half-brother. In August 1067 he and Bleddyn joined Eadric the Wild in an attack upon Herefordshire, which was part of the general resistance to the Conqueror. In 1069 (or 1070?) the two fought the battle of Mechain with Maredudd and Idwal, sons of Gruffydd ap Llywelyn. Though they were victorious, Rhiwallon fell, leaving Bleddyn sole prince of North Wales. His daughter Nest married Rhys ap Tewdwr, and was mother of Nest [q. v.], the mistress of Henry I (Brut y Tywysogion, ed. Rhys and Evans, p. 281).
[Annales Cambriæ; Anglo-Saxon Chronicle; Florence of Worcester; Freeman's Norman Conquest, iv. 110, 183.]