It was Cadfan who, as heir to the throne of his father, Iago ap Beli, took the little Edwin of Deira under his wing and brought him up as his own son. Cadfan fought bravely at the Battle of Caer-Legion (Chester) in 613 when Edwin's sworn enemy, King Ęthelfrith of Bernicia, invaded Gwynedd. When it was over, he found himself to be King. The Battle of Bangor-is-Coed followed in quick succession, and the young monarch showed such leadership that he was, afterwards, declared High-King of the Britons. Edwin, meanwhile, thought it prudent to leave Wales for Mercia, thus protecting his foster-father from further attack.
Cadfan was the "wisest and most splendid of all kings" according to his memorial stone which can still be seen today in the church of Llangadwaladr on Ynys Mon (Anglesey). He died there around 625 (though some say 616). He had been a patron of St.Beuno.