William II, Count of Flanders

William III (1224 – 6 June 1251) was the lord of Dampierre from 1231 and count of Flanders from 1247 until his death.

[1] Margaret inherited Flanders and Hainault in 1244 and immediately the War of the Succession of Flanders and Hainault began between William and his brothers, the Dampierre claimants, and the children of Margaret's first marriage to Bouchard of Avesnes.

In 1246, Louis IX of France intervened to arbitrate the conflict and declared Flanders to William and Hainault to John I of Avesnes.

On 6 June the next year, William died at a tournament in Trazegnies.

[4][a][b] The war began anew with Guy, William's younger brother, taking up Flanders and the Dampierre claim.