 It is believed that Tecwyn was the brother of Saint Tanwg of Llandanwg, Saint Twrog of Maentwrog, Saint Tegai of Llandegai and Saint Baglan of Llanfaglan and Baglan.According to Enwogion Cymru, he was the son of Ithel Hael o Lydaw of Brittany, and arrived in Britain with Saint Cadfan, in the time of Vortigern "who procured wise men and divines from Gaul, now called France, to renovate Christianity in this Island, in consequence of the decay and failure that had befallen the faith in Christ.