Isabella of Navarre, Countess of Armagnac

Isabella of Navarre (1395 – 31 August 1450) was the younger surviving daughter of Charles III of Navarre and his wife Eleanor of Castile. She was a member of the House of Évreux.

Shortly before Isabella's birth, her mother was dealing with problems in Castile, involving her brother John I of Aragon. Eleanor was forced to return to Navarre for her daughter's birth.

Isabella was the sixth of eight children. Her two younger brothers died in childhood, leaving Isabella and her five older sisters. Her sisters included: Joanna (died before inheriting the throne), Blanche (successor of their father) and Beatrix, (married James II, Count of La Marche)

Isabella's maternal grandparents were Henry II of Castile and Juana Manuel of Castile. Her paternal grandparents were Charles II of Navarre and Joan of France, herself daughter of John II of France and Bonne of Bohemia.

Isabella was firstly betrothed to Infante John of Aragon around 1414. Her mother, Queen Eleanor bequeathed her money for the marriage. John later became King of Aragon but broke off his contract with Isabella, in hopes of marrying Joanna II of Naples.

Isabella eventually married on 10 May 1419 John IV of Armagnac. This marriage was John's second marriage, after the death of his first wife Blanche of Brittany, who had left no sons.

Isabella and John had five children:

• Marie of Armagnac (b. 1420–1473), married in 1437 John II of Alençon (b. 1409–1476), Duke of Alençon; maternal great-grandparents of King Henry IV of France.
• John V of Armagnac (b. 1420–1473), Viscount of Lomagne, then Count d' Armagnac, of Fézensac and Rodez. He married illegally to younger sister Isabella, had issue and married secondly to Joan of Foix, also with issue.
• Eleanor (b. 1423–1456), married in 1446 Louis de Chalon (b. 1389; † 1463), Prince d'Orange, Lord of Arlay and Arguel, had issue
• Charles I (b. 1425–1497), Viscount of Fézensaguet, then Count d' Armagnac, of Fézensac and Rodez
• Isabella (b. 1430–1476), Lady of the Four-Valleys, married illegally to brother John and had issue.

Isabella and her husband both died in 1450; she died in August and he died three months later in November, she was around fifty-four at the time of death.