Prince Tysilio was the younger son of King Brychwel Ysgithrog, who, as a prince himself, had discovered Melangell in a valley within his land. The influence of Melangell had obviously remained with Brychwel Ysgithrog and within his kingdom, and had been passed on to his children. As a young child, Tysilio, with his friends and siblings, may have even visited Melangell and been witness to the ‘miracles and various other signs [which were not] lacking for those who called upon her help’.

Tysilio grew up in turbulent times of kingdom wars, and fled his father’s court to become a monk. He spent some time travelling around Wales, teaching and preaching and planting churches, and then became a hermit for some time on Ynys Tysilio in the Menai Straits. He also spent seven years teaching and preaching on Ynys Mon (Anglesey) and planting churches there. The most famous of Tysilio’s churches is on Ynys Mon and is one of the locations mentioned in the longest place name in Britain: Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch. This translates roughly as ‘Church of Mary in the Hollow of the White Hazel near a Rapid Whirlpool and the Church of Tysilio near the Red Cave’.

After the death of Tysilio’s elder brother, who had inherited the throne from their father, his sister-in-law, Queen Gwenwynwyn, wanted to marry Tysilio and have him as king. When he objected to both proposals, his monastery came under the scorn of the queen and suffered persecution from her and her political influence. Eventually, he decided to move to Brittany with a small band of followers. They crossed the Channel and travelled to Saint-Suliac, where Tysilio established another monastery.

Tysilio died in the monastery in Saint-Suliac and was buried there.