Samuel Rawson Gardiner,
A Student's History of England…
“ North-humberland was therefore the first of the three to rise to the foremost place. Till the death of Ælla, the king of Deira, from whose land had been carried off the slave-boys whose faces had charmed Gregory at Rome, Deira and Bernicia had been as separate as Kent and Essex. Then in 588 Æthelric of Bernicia drove out Ælla's son and seized his kingdom of Deira, thus joining the two kingdoms of Deira and Bernicia (see p. 36) into one, under the new name of North-humberland. [2] 9. ”
