In 655, Æthelhere was one of thirty noble warlords who joined with Penda in an invasion of Northumbria, laying siege to Oswiu and the much smaller Northumbrian army.
En 655, Æthelhere era un de trinta nobres guerreiros que se uniron a Penda para invadir Northumbria, pondo asedio a Oswiu e ao moito máis pequeno exército northumbriano.