William of Ypres (c. 1090 – 24 January 1164/1165[1]), styled count of Flanders,[2][3] was King Stephen of England's chief lieutenant during the English civil wars of 1139–54 (known as the Anarchy). He commanded a contingent of Flemish soldiers.
He claimed the county of Flanders upon the death of Charles the Good on 2 March 1127/28.[2]
Though no proof exists of his creation as Earl of Kent by King Stephen, chroniclers describe him as "possessing the county" and "having Kent in his custody".[2] He exercised the same powers over this county as other earls over theirs; though he never adopted the comital style.[2]
He founded the Cisterian house of Boxley circa 1146.[2]
He was an illegitimate son of Philip of Loo, son of Robert I, Count of Flanders and Gertrude of Saxony.[2] He was a claimant in 1119 to the title of Count of Flanders but lost the claim to Charles the Good; and again in 1127, when he lost to William Clito.[2] The chronicle of Galbert of Bruges attributes his failure to his illegitimate birth.[2] He sought the title again the following year (1128) after William Clito's death, but lost to Thierry of Alsace, who banished him from Flanders in 1133.[2]