Anglo-Saxon Chronicle. 839. Text 836AD. This year died [his grandfather] King Egbert (age 66). Him Offa, King of Mercia, and Bertric, the West-Saxon king, drove out of England into France three years before he was king. Bertric assisted Offa because he had married his daughter. Egbert (age 66) having afterwards returned, reigned thirty-seven winters and seven months. Then [his father] Ethelwulf, the son of Egbert, succeeded to the West-Saxon kingdom; and he gave his son Athelstan the kingdom of Kent, and of Essex, and of Surrey, and of Sussex.
Anglo-Saxon Chronicle. 851. This year Alderman Ceorl, with the men of Devonshire, fought the heathen army at Wemburg [Map], and after making great slaughter obtained the victory. The same year King Athelstan and Alderman Elchere fought in their ships, and slew a large army at Sandwich [Map] in Kent, taking nine ships and dispersing the rest. The heathens now for the first time remained over winter in the Isle of Thanet [Map]. The same year came three hundred and fifty ships into the mouth of the Thames; the crew of which went upon land, and stormed Canterbury, Kent [Map] and London; putting to flight Bertulf, king of the Mercians, with his army; and then marched southward over the Thames into Surrey. Here [his father] Ethelwulf and his son [his brother] Ethelbald, at the head of the West-Saxon army, fought with them at Ockley [Map], and made the greatest slaughter of the heathen army that we have ever heard reported to this present day. There also they obtained the victory.
In 852 King Æthelstan of Kent died. He may have been buried at Winchester Old Minster.
Paternal Family Tree: King Æthelstan of Kent
Kings Wessex: Son of King Æthelwulf of Wessex