Although Athelstan was a favoured grandson of Alfred the Great, and the eldest son of King Edward, it seems that he was no longer Edward’s designated heir after the birth of his half-brother, Aelfweard. According to William of Malmesbury, Athelstan left Wessex at some point in his childhood and moved to Mercia to be brought up by his aunt, Aethelflaed, the Lady of the Mercians and the daughter of Alfred the Great. By this time Mercia was no longer an independent kingdom; it was subservient to Wessex and under the day-to-day rule of Ealdorman Aethelred, the so-called Lord of the Mercians and his wife, Lady Aethelflaed. Once he had come of age Athelstan went to war and helped his aunt and uncle to free northern Mercia from Danish control.  Ealdorman Aethelred died in 911 and Aethelflaed ruled Mercia alone, probably with assistance from Athelstan, until her own death in 918. Between 918 and 924 Athelstan was probably based in Mercia ruling the Midlands on behalf of his father.