GUILLAUME [I] de Bellême, son of IVES Seigneur de Bellême & his wife Godehildis --- (-[1031]). André de Fleury´s Vita Gauzlini records that “Ivo Belesmensis” donated “Magniacum” to Fleury, but that after his death “Willelmus eius filius” reclaimed the property, and in a later passage that “Willelmus Belesmensis” donated “abbatiam Longeilegium” [Lonlay, Le Mans][30].Sire d'Alençon. Guillaume of Jumièges records that Robert II Duke of Normandy besieged “Willelmus Belesmensis, Yvonis filius...ex castro Alentio quod beneficio tenebat iure”, who had rebelled, and forced his submission (although he rebelled again later)[31]. "Ivo" founded Notre-Dame de Bellême, for the souls of himself "conjugisque mee Godehildis, sive filiis meis vel genitoribus meis", by undated charter, confirmed after his death by "Willelmus et Godehildis mater mea"[32]. He founded the abbey of Dame-Marie [1023/26][33]. Europäische Stammtafeln[34] inserts an additional generation between "Guillaume de Belesme, fils d'Yves" and the four brothers who are reported by Guillaume de Jumièges as his sons: "Guillaume [I] "Talvas" "princeps" de Bellême, Sire d'Alençon, 1004-1013 iuvenis, erbaut Domfront, gründet um 1020 abbaye de Lonlay (-Domfront [1031], burNotre-Dame-sur-l'Eau" recording his wife as "Mathilde, [1020]". From a chronological point of view, this appears unlikely to be correct, especially if the two brothers Ives Bishop of Sées and Robert were sons of the older Guillaume as shown in the same table of Europäische Stammtafeln (see below). The primary sources on which this is based have not yet been identified, but until more information emerges it appears preferable to show this family as reported by Guillaume de Jumièges. La Chronique Manuscrite de Normandie records that Robert II Duke of Normandy granted Alençon to "à Belesme ung seigneur nommé Guillaume" who rebelled against the duke who besieged the castle and captured Guillaume[35].
m MATHILDE Dame de Condé-sur-Noireau, daughter of ---. La Chronique Manuscrite de Normandie states that the mother of the sons of "à Belesme ung seigneur nommé Guillaume" was "Mehault du lignaige de Guennelon"[36]. The primary source which confirms her family origin more precisely has not yet been identified.
Guillaume & his wife had five children