825. Battle of Ellendun (Wroughton, Wilts.): Ecgberht of Wessex defeats Beornwulf of Mercia
Æthelwulf of Wessex drives Bealdred out of Kent
People of Kent, Surrey, South Saxons and East Saxons submit to Æthelwulf
The Anglo-Saxon Chronicle states that Ecgberht fought Beornwulf of Mercia at Ellendun (Wroughton) and that Ecgberht won and there was a great slaughter there. Then Ecgberht sent his son Æthelwulf and bishop Ealhstan and ealdorman Wulfheard to Kent, with a large force, and they drove Bealdred north across the Thames, and the people of Kent and Surrey and the South Saxons and the East Saxons submitted to Æthelwulf because they had been wrongfully forced away from his kinsmen.
A late 11th-century manuscript of the Anglo-Saxon Chronicle notes under 784 that Ealhmund ruled in Kent, and that Ealhmund was Ecgberht's father, who was Æthelwulf's father. This makes clear the link between the West Saxon ruling house and Kent and the south-east. Since we know that members of the main West Saxon ruling family were not in power in Wessex between Ine's death in 726 and Ecgberht's accession in 802, the most likely explanation is that one of these exiled West Saxon æthelings gained a foothold in Kent while Cynewulf was ruling in Wessex (757-86). (See also Keynes, p.3, n.8)
S. Keynes, "King Alfred and the Mercians", in M. Blackburn and D. Dumville (edd.), Kings, Currency and Alliances: History and Coinage of Southern England in the Ninth Century (Woodbridge: 1998), pp.1-45