• Born: 1101, Rouen, Haute-Normandie, France
• Married (1): 1123
• Married (2): Jan 1127
• Died: 27 Jul 1128, Abbey de Saint-Bertin

  Research Notes:

Guillaume of Jumièges records that ”Robertus” married “Sibyllam...sororem Willelmi comitis Conversanæ”, by whom he had “unum filium...Willelmum”. His parentage is stated by Orderic Vitalis, who specifies that he was born in Rouen in the third year after his parents' marriage. After his father was captured by Henry I King of England, the king entrusted Guillaume to Hélie de Saint-Saens (who was married to Guillaume's illegitimate half-sister). According to Orderic Vitalis, after King Henry "returned victorious to England", he commanded Robert de Beauchamp Vicomte d'Arques to arrest Guillaume, who was taken into "exile among foreigners" by Hélie and helped by Robert de Bellême. Guillaume was eventually given refuge by Baudouin VII Count of Flanders "who fought resolutely on his behalf until he died". "Karolo et Wilhelmo nepotibus comitis" were named in the grant to Saint-Bertin of "Balduinus Roberti iunioris filius Flandrensium comes" dated 1119. Guillaume continually challenged the authority of his uncle King Henry in Normandy, with support from Louis VI King of France and many rebel Norman barons. King Louis granted Pontoise, Chaumont, Mantes and the Vexin to Guillaume on his second marriage. Guillaume also received the support of his father-in-law, who was indignant that King Henry had retained the dowry of his other daughter Alice, after her husband King Henry's son had been drowned in the Blanche Nef [White Ship] in 1120.

Following the assassination of Charles Count of Flanders, Louis VI King of France convened a meeting of Flemish barons at Arras where they elected Guillaume 21 Mar 1127 as GUILLAUME I "Clito" Count of Flanders, although he lacked any hereditary right. He was opposed by his uncle King Henry who bribed supporters in Gent and eastern Flanders. Lille rebelled against his authority 1 Aug 1127, followed by Saint-Omer 8 Feb 1128. Guillaume's rival Thierry d'Alsace captured Lille, Furnes and Gent and was recognised as Count of Flanders at Bruges 30 Mar 1128.

Guillaume besieged Aalst in Jul 1128, helped by Godefroi Duke of Lower Lotharingia, but was injured and died from his wounds. The necrology of Saint-Nicaise de Meulan records the death "IV Kal Aug" of "Guillelmus comes Flandrensis filius Roberti ducis Normannie". ¹