Ieuaf was a son of King Idwal Foel.
Upon his father's death in battle against the Anglo-Saxons in 942, he and his brother Iago ab Idwal were driven from their kingdom by their uncle Hywel Dda of Deheubarth, who took the crown for himself.
On Hywel's death in 950, Ieuaf and Iago were able to drive out Hywel's sons, their cousins, at the Battle of Carno and reclaim the kingdom.
The southern princes were finally defeated at the Battle of Llanrwst and chased back to Ceredigion.
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