 Having overwintered in Isles, Magnús left for Norway in the summer, only to make his return nearly four years later, in 1102 or 1103. Once re-established on Mann, Magnús entered into an alliance with Ua Briain, formalised through the marriage between Magnús's young son, Sigurðr (died 1130), and Ua Briain's daughter, Bjaðmunjo (fl. 1102 / 1103). Magnús, therefore, appears to have intended for Sigurðr to rule over his recently-won territories. Unfortunately for Ua Briain, and his long-term ambitions in Ireland and the Isles, Magnús was slain in Ulster in 1103, whereupon Sigurðr immediately repudiated his bride and returned to Norway. Although Ua Briain was able to regain control of Dublin, and still held considerable influence in the Isles, Magnús' death appears to have left a power vacuum in the region that he was unable to fill.
