The son of Jean III d'Harcourt and Alix de Brabant, Jean IV, first comte d'Harcourt, marries Isabeau de Parthenay. Their sons Guillaume d'Harcourt is the seigneur of La Ferté-Imbault. From his marriage to Blanche de Bray, Dame de Cernon, they had one daughter, Jeanne d'Harcourt, Dame de La Ferte-Imbault, who married Hugues de Montmorency. Their sons, Louis and Antoine, died at the Battle of Azincourt in 1415 for the first, and Verneuil in 1424 for the second. Their sister, Catherine de Montmorency, inherits the vast estate of La Ferté-Imbault after the death of her two brothers.