Together, Dafydd and Rhodri attacked and killed their brother Hywel ab Owain Gwynedd that same year.
Other brothers, Iorwerth Drwyndwn and Cynan ab Owain Gwynedd, were killed in 1174, removing two more contenders for the throne.
He was now sole ruler of Gwynedd and that same year he married Emma (or Emme) of Anjou, the half-sister of King Henry II of England, in summer 1174.
He had a castle at Rhuddlan where Gerald of Wales spent a night in 1188 on his journey round Wales with Baldwin of Forde (Archbishop Baldwin): "Having crossed the river Conwy, or rather an arm of the sea, under Deganwy, leaving the Cistercian monastery of Conwy on the western bank of the river to our right hand, we arrived at Ruthlan, a noble castle on the river Cloyd, belonging to David, the eldest son of Owen, where, at the earnest invitation of David himself, we were handsomely entertained that night".
[1][2]In 1194, Dafydd faced a new threat from his nephew, Llywelyn ap Iorwerth, who defeated him at the battle of Aberconwy with the aid of his cousins, the sons of Cynan ab Owain Gwynedd, drove him from most of his possessions and imprisoned him in 1197.