Sources: Royal Descents; A. Roots 178; Young; Dakota; Kraentzler 1447. Roots: Rhiwallon ap Cynfyn of Powys. Young: Rhiwallon ap Cynfyn ap Gwerstan,prince of Powys. K: Rhiwallon ap Cynvyn, killed at the Battle of Mechain in 1068. Descents: Rhywallon, Prince of Powys, died 1070. Dakota: Rhysivallan apCynfyn and brother of Bleddyn, King of Powys. A. Families says died 1073. King Rhiwallon ap Cynfyn was killed at the battle of Mechain.