Æthelred rose to power in the wake of his half-brother’s Edward’s murder at Corfe. The younger son of King Edgar, aged no more than twelve years old, Æthelred was anointed king ‘with much rejoicing’ at Kingston, Surrey, on 4 May 979, according to the Anglo-Saxon Chronicle.
Hicklin, Alice. "Æthelred 'the Unready' becomes King". The Literary Encyclopedia. First published 29 June 2016
[http://www.litencyc.com/php/stopics.php?rec=true&UID=1942, accessed 29 June 2016.]