Gruffudd ap Gwenwynwyn

In 1263, he agreed to transfer his allegiance to Llywelyn under threat of being stripped of his lands, and this was confirmed at the Treaty of Montgomery in 1267.

Dafydd was with Llywelyn at the time, and it was arranged that Owain would come with armed men on 2 February to carry out the assassination; however, he was prevented from doing so by a snowstorm.

There have been suggestions that his eldest son Owain may have been involved in the killing of Llywelyn at Cilmeri in December that year.

For his loyalty to Edward I, the king permitted Baron de la Pole to begin building (or re-building) Powis Castle.

Owain divided the lands he inherited with his brothers, by arrangements later recorded in detail in the Calendar of Patent Rolls for 1342, pages 496–7.