 After his death, his kingdom was split between Harald Hardrada in Norway and Sweyn Estridsson in Denmark.Magnus was an illegitimate son of King Olaf Haraldsson (later St. Olaf), by his English concubine Alfhild, originally a slave (thrall) of Olaf's queen Astrid Olofsdotter.Born prematurely, the child was weak and unable to breathe for the first few minutes, and he was probably not expected to survive.