William FitzWilliam

William FitzDuncan had one illegitimate son by Mistress (1): 7. WILLIAM . The primary source which confirms his parentage has not yet been identified. m (1138) ---. (Medieval Lands, " DESCENDANTS of WILLIAM FitzDuncan")

Cawley is here being parsimonious in his assessment of William FitzDuncan's activities - he had a reputation for "getting around" and leaving a trail of offspring in his wake. That he had more than one mistress and more than one resulting child is highly probable. Maven.

Referred to as William FitzWilliam to distinguish him from the numerous Mac Williams.