Prince Tyslio (or Sulio) was the second son of Brochfael Ysgythrog (of the Tusks). He fled his father's court at an early age to throw himself on the mercy of Abbot Gwyddfarch of Caer-Meguaidd (Meifod) and beg to become a monk. A Powysian warband was sent to retrieve him, but King Brochfael was eventually persuaded that his son should be allowed to stay. Fearful of further trouble, however, Tysilio set up his base at a hermitage on Ynys Tyslio (Church Island) in the Menai Straits and became a great evangeliser on Ynys Mon (Anglesey). He spent seven years there before returning to Caer-Meguaidd (Meifod) and succeeding as Abbot. Tyslio rebuilt the Abbey Church and things were peaceful for a while. However, after the death of Tysilio's brother, his sister-in-law, Queen Gwenwynwyn, desired to marry him and place him on the throne of Powys. Objecting to both proposals, the saint refused and found his monastery persecuted by the state. So he resolved to leave for Brittany with a handful of followers. Tysilio travelled through Dyfed and across the Channel to St. Suliac where he established a second monastery. He died and was buried there in 640.