It was during this exile that his father probably adopted the surname de la Pole meaning "of the Pool" and referring to the old name for Welshpool which had become his family's capital.
However, good relations between Powys Wenwynwyn and Gwynedd were short-lived as Owen and his father were soon implicated in an assassination attempt on the Prince of Wales in 1274.
In 1284, following the Conquest of Wales by Edward I, the de la Pole family surrendered their princely pretensions, but received back their principality in "free barony" as the marcher lordship of Powys.
Only William left children and they enjoyed the Lordship of Mawddwy and the majority of Mallwyd for several generations, before it was divided between coheirs in the early 16th century.
After his death the lordship of Powis passed to his son Griffith, who died in childless in 1309, and then to his daughter Hawise and her descendants from her marriage to John Charleton, 1st Baron Cherleton.