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

William II of Dampierre William II (1196 – 3 September 1231) was the lord of Dampierre from 1216 until his death. He was the son of Guy II, constable of Champagne, and Mathilde of Bourbon.Theodore Evergates, ''The Aristocracy in the County of Champagne, 1100-1300 ...

and

Margaret II of Flanders Margaret, often called Margaret of Constantinople (1202 – 10 February 1280), ruled as Countess of Flanders during 1244–1278 and Countess of Hainaut during 1244–1253 and 1257–1280. She was the younger daughter of Baldwin IX, Count of ...

. Margaret inherited Flanders and Hainault in 1244 and immediately the

War of the Succession of Flanders and Hainault {{Infobox military conflict , conflict = {{PAGENAME , width = , partof = , image = Carte des comtés de Flandre et de Hainaut sous la comtesse Jeanne de Constantinople (1200-1244).png , image_size = 300px , alt ...

began between William and his brothers, the Dampierre claimants, and the children of Margaret's first marriage to

Bouchard of Avesnes Burchard IV or Bouchard IV (1182–1244) was the lord of Avesnes and Étrœungt. He was the son of James of Avesnes and Adela of Guise and brother of Walter, Count of Blois.(FR)Henri Platelle, ''Présence de l'au-delà: une vision médiévale ...

. Margaret favoured William and declared him her heir. In 1246, Louis IX of France intervened to arbitrate the conflict and declared Flanders to William and Hainault to

John I of Avesnes John of Avesnes (1 May 1218 – 24 December 1257) was the count of Hainaut from 1246 to his death. Life Born in Houffalize, John was the eldest son of Margaret II of Flanders by her first husband, Bouchard IV of Avesnes. As the marriage of Marg ...

. Margaret officially invested William as count in 1247. In November of that year, William married

Beatrice of Brabant Beatrice of Brabant (1225 – 11 November 1288), was a Landgravine consort of Thüringia and a Countess consort of Flanders, married first to Henry Raspe, Landgrave of Thuringia, and later to William II, Count of Flanders. Biography Béatr ...

, daughter of

Henry II, Duke of Brabant Henry II of Brabant ( nl, Hendrik, french: Henri; 1207 – February 1, 1248) was Duke of Brabant and Lothier after the death of his father Henry I in 1235. His mother was Matilda of Boulogne. Henry II supported his sister Mathilde's son, ...

and

Marie of Hohenstaufen Maria of Swabia (1199/1200 – 29 March 1235) was a member of the powerful Hohenstaufen dynasty of German kings. Family Maria of Hohenstaufen was born in Arezzo, Tuscany, Italy around 1199/1200. She was the second daughter of Philip of Swabia an ...

. They had no children. Meanwhile, the fight continued over Namur between the Dampierres and the Avesnes. On 19 May 1250, peace was signed. On 6 June the next year, William died at a

tournament A tournament is a competition involving at least three competitors, all participating in a sport or game. More specifically, the term may be used in either of two overlapping senses: # One or more competitions held at a single venue and concentr ...

in Trazegnies. The war began anew with Guy, William's younger brother, taking up Flanders and the Dampierre claim.

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* * * * * * * William III Counts of Flanders 1224 births 1251 deaths Assassinated royalty 13th-century peers of France 13th-century people from the county of Flanders Christians of the Sixth Crusade {{France-noble-stub