• Born: 1 May 1218, Houffalize, Luxembourg, Belgium
• Married: 9 Oct 1246, Frankfort-am-Main, Hessen-Nassau
• Died: 24 Dec 1257, Valenciennes, Hainault, Belgium

  Research Notes:

The Genealogica Comitum Flandriæ Bertiniana names "Iohannem et Balduinem" as the two sons of "Buchardi Avenennsis [et] Margaretæ". His date of birth is indicated by the charter dated Jan [1234/35] under which Louis IX King of France records that “Johannes, Burchardi de Avesnis militis filius” was 16 years old “mense aprili preterito”. His parentage is recorded by Matthew of Paris in his description of the background to the war in Flanders in 1254. He and his brother were brought up in France after his parents separated, considered illegitimate because of the Papal annulment of their marriage. After his mother succeeded in 1244 as Ctss of Flanders and Hainaut, Jean claimed his inheritance. Louis IX King of France ruled in 1246 that Jean should receive Hainaut while Flanders should go to his Dampierre half-brother.

He therefore succeeded in 1246 as JEAN I Comte de Hainaut. He attempted unsuccessfully to obtain imperial recognition of his claim to Flanders but accepted the 1246 decision when Willem II Count of Holland received homage, as king of Germany, for imperial Flanders from Guillaume de Dampierre. He and his brother were legitimated by the Pope in 1251, on the request of their mother. His mother offered the county of Hainaut to Charles de France Comte d'Anjou in order to obtain his military intervention against Willem II Count of Holland. Comte Charles besieged Valenciennes, but a truce was negotiated between all parties 26 Jul 1254, which included an agreement to submit the dispute to Louis IX King of France for adjudication. King Louis required his brother to renounce any claim to Hainaut in his judgment of 1256. ¹