GUILLAUME [IV] de Saint-Omer (-in Palestine [1191/92]). "Willelmo nepote castellani" is named in a charter dated 1157[765]. Châtelain de Saint-Omer. "…Willelmi castellani de Sancto Audomaro…" signed the charter dated [Apr/May] 1175 under which Philippe Count of Flanders confirmed pasturage rights of the abbey of Saint-Bertin[766]. "Willelmus Audomarensis castellanus…cum Ida uxore mea et Matilde matre mea" regulated the conditions of the inhabitants of Froland and Hofland by charter dated 25 Apr 1178[767]. Seigneur de Fauquemberques. The Chronicon Hanoniense names "Willelmus castellani Sancti Audomari" among those who died in Palestine in [1191][768]. m ([1170/71]) as her second husband, IDA d'Avesnes, widow of ENGUERRAND Comte de Saint Pol, daughter of NICOLAS Seigneur d'Avesnes & his wife Mathilde de la Roche [Namur] (-[1205]). The primary source which confirms her first marriage has not yet been identified. The Chronicle of Alberic de Trois-Fontaines names (in order) "Iacobum et Idam castellanam Sancti Audemari" as children of "Nicolao de Avenes" & his wife[769]. The Chronicon Hanoniense refers to the daughter of "Nicholaus filius [Walteri…de Avethnes]" & his wife as "Willelmo…castellano Sancti Audomari maritatam"[770]. The late 13th century genealogy by Balduinus de Avennis records that "Nicolaus Plukellus…filiam…Ydam" married "castellano Sancti Audomaro Wilelmo"[771]. Guillaume [IV] & his wife had ten children