Æthelstan (/ˈæθəlstæn/; died c. 852) was the King of Kent from 839 to 851. He served under the authority and overlordship of his father, King Æthelwulf of Wessex, who appointed him. The late D, E and F versions of the Anglo-Saxon Chronicle describe Æthelstan as Æthelwulf's brother, but the A, B and C versions, and Æthelweard's Chronicon, state that he was Æthelwulf's son. Some historians have argued that it is more probable that he was a brother, including Eric John in 1966 and Ann Williams in 1978. However, in 1991 Ann Williams described him as Æthelwulf's son, and this is now generally accepted by historians, including Frank Stenton, Barbara Yorke, and D. P. Kirby.
When Æthelwulf became King of the West Saxons in 839 on the death of his father, Ecgberht, he appointed Æthelstan to rule over Kent, Essex, Surrey and Sussex. He is styled king in the Anglo-Saxon Chronicle and Æthelweard's chronicle calls him "King of the Dwellers in Kent, of the East Saxons, of the South Saxons and of Surrey". He attested a number of his father's charters as king in the 840s.