Matthew of Alsace

Matthew of Alsace (c. 1137–1173) was a younger son of Thierry of Flanders and Sibylla of Anjou. In 1160 Henry II of England arranged his marriage to Mary of Blois, abbess of Romsey and heiress of Boulogne, making him count of Boulogne; because Mary was a nun, he was excommunicated.

Henry's refusal to cede Mortain led Matthew to ally with Louis VII of France. Separated from Mary in 1170, he ruled through their daughters Ida and Matilda. In 1173 he joined Henry the Young King's revolt and, invading Normandy with his brother Philip of Flanders, was mortally wounded by a crossbow at Driencourt on 25 July.