Early in his career, Fergus bound himself to the Isles in the form of a marital alliance between Affraic and Óláfr, the reigning King of the Isles. Although the union itself is not dated in contemporary sources, the Scandinavian sojourn undertaken the couple's son in 1152 suggests that the marriage was arranged in the 1130s or 1140s. The alliance forged between Óláfr and Fergus gave the former's family valuable familial-connections with the English Crown, one of the most powerful monarchies in western Europe. As for Fergus, the union bound Galloway more tightly to a neighbouring kingdom from which an invasion had been launched during the overlordship of Magnús Óláfsson, King of Norway. The alliance with Óláfr also ensured Fergus the protection of one of Britain's most formidable fleets, and further gave him a valuable ally outwith the orbit of the Scottish Crown.