Harthacnut, the only legitimate son of Cnut, had been away defending Denmark from Magnus of Norway at the time of his father's death, and had been happy to allow his half-brother Harald to rule in England as regent. He had come to an arrangement with Magnus whereby the first of them to die without an heir would leave his kingdom to the other. Magnus and his successor Harald Hardrada took this to include England and staked their claim to the English throne. Harthacnut responded by designating an heir of his own, Æthelred's surviving son Edward.
Predecessor: King Harald I, his half-brother
Successor: Edward the Confessor
Father: Cnut I