after oswine's death, athelwald became king. it is uncertain whether oswiu (who was athelwald's uncle) installed him as king or whether athelwald took the kingship in opposition to oswiu. at some point he allied himself with oswiu's enemy, penda of mercia. he guided penda during his invasion of northumbria in 655. but, when the armies of oswiu and penda met on 15 november at the battle of the winwaed, athelwald withdrew to safety. penda was defeated and killed. perhaps in part because of this desertion, and afterward athelwald was not heard of again.