King of East Anglia 827-839
Athelstan appears as the king of East Anglia in the year 827 when he requested the assistance of Ecgberht of Wessex in freeing himself and his kingdom from the rule of the Mercians. (Indeed there are some who do say that this Athelstan was the son of Ecgberht.)
Athelstan defeated the Mercians and slew their king Beornwulf and ruled East Anglia for twelve years. It is believed that the Aethelweard who succeeded him was his son.
King of East Anglia 879-890
It should also be remembered that there was yet another Athelstan destined to be ruler of East Anglia, as "Athelstan" was the baptismal name taken by the Viking warrior Guthrum who ruled the kingdom between the years 879 and 890.