Question: Alhfrith was King of Deira under his father, who was King of Bernicia following the death of which brother in 642?

Context paragraphs:
Edwin of Northumbria: Edwin (Old English: "Ēadwine" ; c. 586 – 12 October 632/633), also known as Eadwine or Æduinus, was the King of Deira and Bernicia – which later became known as Northumbria – from about 616 until his death.  He converted to Christianity and was baptised in 627; after he fell at the Battle of Hatfield Chase, he was venerated as a saint.

Ælla of Deira: Ælla (Ella, Ille) (died 588), is the first certain king of Deira.  One of his sons was Edwin of Northumbria and his daughter Acha married Æthelfrith of Bernicia.

Wilfrid: Wilfrid (c.  633 – c. 709) was an English bishop and saint.  Born a Northumbrian noble, he entered religious life as a teenager and studied at Lindisfarne, at Canterbury, in Gaul, and at Rome; he returned to Northumbria in about 660, and became the abbot of a newly founded monastery at Ripon.  In 664 Wilfrid acted as spokesman for the Roman position at the Synod of Whitby, and became famous for his speech advocating that the Roman method for calculating the date of Easter should be adopted.  His success prompted the king's son, Alhfrith, to appoint him Bishop of Northumbria.  Wilfrid chose to be consecrated in Gaul because of the lack of what he considered to be validly consecrated bishops in England at that time.  During Wilfrid's absence Alhfrith seems to have led an unsuccessful revolt against his father, Oswiu, leaving a question mark over Wilfrid's appointment as bishop.  Before Wilfrid's return Oswiu had appointed Ceadda in his place, resulting in Wilfrid's retirement to Ripon for a few years following his arrival back in Northumbria.

Eanfrith of Bernicia: Eanfrith (590–634) was briefly King of Bernicia from 633 to 634.  He was the son of Æthelfrith, a Bernician king who had also ruled Deira to the south before being killed in battle around 616 against Raedwald of East Anglia, who had given refuge to Edwin, an exiled prince of Deira.

Œthelwald of Deira: Œthelwald was a King of Deira (651–c. 655).  He was the son of King Oswald of Northumbria, who was killed at the Battle of Maserfield in 642.

Alhfrith: Alhfrith or Ealhfrith (c. 630 – c. 664) was King of Deira under his father Oswiu, King of Bernicia, from 655 until sometime after 664.  Appointed by Oswiu as a subordinate ruler, Alhfrith apparently clashed with his father over religious policy, which came to a head at the Synod of Whitby in 664.  After this, Alhfrith disappears from the historical record.

List of monarchs of Northumbria: Northumbria, a kingdom of Angles, in what is now northern England and south-east Scotland, was initially divided into two kingdoms: Bernicia and Deira.  The two were first united by Aethelfrith around the year 604, and except for occasional periods of division over the subsequent century, they remained so.  The exceptions are during the brief period from 633 to 634, when Northumbria was plunged into chaos by the death of King Edwin in battle and the ruinous invasion of Cadwallon ap Cadfan of Gwynedd.  The unity of the Northumbrian kingdoms was restored after Cadwallon's death in battle in 634.

Æthelfrith: Æthelfrith (died c. 616) was King of Bernicia from c. 593 until his death.  Around 604 he became the first Bernician king to also rule the neighboring land of Deira, giving him an important place in the development of the later kingdom of Northumbria.  He was especially notable for his successes against the Britons and his victory over the Gaels of Dál Riata.  Although he was defeated and killed in battle and replaced by a dynastic rival, his line was eventually restored to power in the 630s.

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.  One of the sons of Æthelfrith of Bernicia, he became king following the death of his brother Oswald in 642.  Unlike Oswald, Oswiu struggled to exert authority over Deira, the other constituent kingdom of medieval Northumbria, for much of his reign.

Manasseh of Judah: Manasseh ( ; "Mənaššeh"; Akkadian: "Menašši" (written "me-na-si-i") ; Greek: Μανασσῆς "Manassís"; Latin: "Manasses" ) was a king of the Kingdom of Judah.  He was the only son of Hezekiah with Hephzibah.  He became king at the age of 12 and reigned for 55 years ( ; ).  Edwin Thiele has concluded that he commenced his reign as co-regent with his father Hezekiah in 697/696 BC, with his sole reign beginning in 687/686 BC and continuing until his death in 643/642 BC.  William F. Albright has dated his reign from 687–642 BC.

Supporting paragraphs: Alhfrith Oswiu
Answer: Oswald