Alhfrith was King of Deira under his father, who was King of Bernicia following the death of which brother in 642?
Oswiu: Oswiu, also known as Oswy or Oswig (Old English: "Ōswīg" ) (c. 612 – 15 February 670), was King of Bernicia from 642 until his death. Oswiu:  One of the sons of Æthelfrith of Bernicia, he became king following the death of his brother Oswald in 642.
i don't know