John III, Duke of Brittany

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John III
The funeral of John III
Duke of Brittany
Reign	27 August 1312 – 30 April 1341
Predecessor	Arthur II
Successor	disputed between: John of Montfort and Joanna with Charles I
Born	8 March 1286 Château de Champtoceaux
Died	30 April 1341(1341-04-30) (aged 55) Caen
Burial	Notre-Dame des Carmes
Spouses	Isabella of Valois ​ ​ (m. 1297; died 1309)​ Isabella of Castile ​ ​ (m. 1310; died 1328)​ Joan of Savoy ​ (m. 1329)​
House	Dreux
Father	Arthur II, Duke of Brittany
Mother	Marie, Viscountess of Limoges

John III the Good (in Breton Yann III, in French Jean III; 8 March 1286 – 30 April 1341) was Duke of Brittany, from 1312 to his death and 5th Earl of Richmond from 1334 to his death. He was the son of Arthur II, Duke of Brittany, and his first wife Marie, Viscountess of Limoges.^[1] John was strongly opposed to his father's second marriage to Yolande and attempted to contest its legality.

In 1297, John married Isabella of Valois,^[2] eldest child of Charles, Count of Valois and his first wife Margaret of Naples. At the time of their marriage John was eleven years old and his bride five. She died childless in 1309.

In 1310, John married his second wife, Isabella of Castile.^[1] She died childless in 1328.

In 1329, John married his third wife Joan of Savoy.^[1] He predeceased his third wife by three years and died childless. He was unwilling to cede the Duchy of Brittany to his half-brother John of Montfort, son of his hated step-mother Yolande. He wished to leave the duchy to the French King Philip VI, but his nobles objected. The marriage of his niece Joanna of Dreux to Charles of Blois gave Charles a plausible claim to the duchy, but the matter was unresolved at John's death.

After his death, John of Montfort claimed his rights as duke of Brittany, but King Philip VI supported the Blois faction, and the Breton War of Succession (1341–1364) was triggered. The Breton Civil War was fought between the House of Blois and the House of Montfort. It became part of the Hundred Years' War, as England supported the Montfort faction, which won, against the House of Blois, which was supported by France.

• 
  Coat of arms as duke until 1316
• 
  In 1316, he simplified his coat of arms to plain ermine. This is still the arms of Brittany.

• Dukes of Brittany family tree

• Jones, Michael (1988). Creation of Brittany: A Late Medieval State. Hambledon Press.
• Morvan, Frederic (2009). La Chevalerie bretonne et la formation de l'armee ducale (in French). Presses Universitaires de Rennes.

• Inquisition Post Mortem #355, dated 1341.