Under the reign of his half-uncle Alexander I, it is highly likely that William was regarded as a viable tánaiste (i.e. "designated heir"),[citation needed] but Henry I of England supported David.
[citation needed] William repeatedly leads the lists of witnesses appearing in Scottish royal charters in the reigns of Alexander I and David I.
It is feasible that this grant had something to do with the coming of age of David's son, Prince Henry and may also be a factor in his marriage to a daughter of Óengus.
As well as being the ruler of Moray, William controlled the English lands of Allerdale, Skipton and Craven, making him one of the greatest barons of northern England.
[citation needed] Domnall mac Uilleim was killed on 31 July 1187 in an uprising against King William the Lion.