Arthur III, Duke of Brittany

Arthur III (in Breton Arzhur III) (24 August 1393 – 26 December 1458), known as the Justicier and as Arthur de Richemont, was Lord of Parthenay and titular Count (Earl) of Richmond in England and for eleven months at the very end of his life, Duke of Brittany and Count of Montfort after inheriting those titles upon the death of his nephew.

Life
Arthur was a younger son of Duke John V and his third wife Joanna of Navarre, and so a member of the Ducal House of Montfort. Arthur was born at the Château de Suscinio.

Just a year before his own death, Arthur succeeded his nephew Peter II as Duke. Arthur was also titular Earl of Richmond; the earldom had often been granted to the Dukes of Brittany, but after the death of Arthur's father, the English refused to recognize his heirs as earls. Nevertheless, they continued to style themselves "Count of Richmond", while the English title was given to John, Duke of Bedford, Plantagenet (1389–1435) in 1414.

Arthur was an important figure at the French court during the Hundred Years' War, even before becoming Duke of Brittany.

Arthur sided with the Armagnac faction against the Burgundians during their civil conflict in France which lasted from 1410 to 1414. He fought at the Battle of Agincourt on 25 October 1415, where he was wounded and captured. He was released by the English in 1420 and helped persuade his brother, Duke John, to sign the Treaty of Troyes. In 1422, the English created him Duke of Touraine. However, he subsequently returned to the allegiance of the Dauphin in 1424, was made Constable of France with support from Yolande of Aragon in 1425.

As Constable of France he fought alongside the charismatic Joan of Arc during her victory at the Battle of Patay on 18 June 1429. Arthur was known for his tenacity and bad temper; the negative aspects of his personality had led to his expulsion from the court in 1427. By 1435 he regained influence at the French court and then helped arrange the Treaty of Arras between Charles VII of France and Philip III, Duke of Burgundy. This treaty cemented the peace between France and Burgundy, leading to the eventual defeat of the English. He was commander of the French army at the Battle of Formigny on 15 April 1450, the next-to-the-last battle of the Hundred Years' War which sealed the reconquest of Normandy.

Family
Arthur was married three times.

His wives were as follows:
 * 1) married in Dijon on 10 October 1423 Margaret of Burgundy (d. 1441), daughter of John the Fearless, Duke of Burgundy and widow of Dauphin Louis, Duke of Guyenne.
 * 2) married in Nérac c. 29 August 1442 Joan of Albret (d. 1444), daughter of Charles II, Count of Dreux
 * 3) married on 2 July 1445 Catherine of Luxembourg-Saint-Pol (d. 1492), daughter of Peter of Luxembourg, Count of Saint-Pol

Arthur also had a natural daughter named Jacqueline who was legitimatized in 1443.

Succession
Arthur died with no known legitimate issue. He was succeeded as Duke of Brittany by his nephew Francis II, Count of Étampes.