Harald, probably the second son of King Cnut and his first wife, Ælfgifu of Northampton, held the English throne after the death of his father in 1035 and until his own (apparently sudden) death in 1040.
His birth can probably be dated to between that liaison (c. 1013-14?) and Cnut's subsequent marriage to Emma in 1017 (presumably following the repudiation of his first wife). His youth coincided with the years of supremacy of his father's second wife and her son, Harthacnut, and he spent this time in obscurity either in England or in Scandinavia.
He re-emerges in the historical record after the death of his father in 1035, and it is clear that he entered into a struggle with the allies of his half-brother …
Bolton, Timothy. "Reign of King Harald Harefoot". The Literary Encyclopedia. First published 05 May 2006
[https://www.litencyc.com/php/stopics.php?rec=true&UID=1667, accessed 23 February 2019.]