His birth is recorded in the Chronicle of Saint-Maixent for the year 1099: Willelmo comiti natus est filius, equivoce Guillelmus vocatus ("a son was born to Count William, named William like himself").
O seu nacemento quedou rexistrado na Cronica de Saint-Maixent no ano 1099: Willelmo comiti natus est filius, equivoce Guillelmus vocatus ("ao conde Guillerme naceulle un fillo, púxoselle de nome Guillerme, coma el.").