GUILLAUME [III] de Saint-Omer, son of GUILLAUME [II] Châtelain de Saint-Omer & his wife Mélisende de Picquigny (-[1170/25 Apr 1178]). The Historia Comitum Ghisnensium names (in order) "Willermum…Hostonem, Gerardum…Hugonem de Falkenberga, Walterum" as the five sons of "Willelmus Andomarensis castellanus" & his wife, specifying that Guillaume was later "Audomarensem castellanum"[773]. 1132/70. Châtelain de Saint-Omer. It is assumed that Gauthier appointed his brother Guillaume as his deputy in the châtellenie de Saint-Omer before travelling east. According to later charters, Gauthier continued to use the title Châtelain de Saint-Omer (see JERUSALEM NOBILITY). "…Willelmi castellani Sancti Audomari…" signed the charter dated 22 Jan [1164/65] under which Philippe Count of Flanders confirmed a 22 Aug 1128 donation by his father, Count Thierry, to the town of Saint-Omer[774]. A charter dated 1172 records a dispute between "Willelmum castellanum Sancti Audomari" and the abbey of Saint-Bertin[775].
m MATHILDE, daughter of --- (-after 25 Apr 1178). "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[776].
Guillaume [III] & his second wife had two children