Facts and Events
'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. He was the son of Duke Arthur II and Mary of Limoges, his first wife. John was strongly opposed to his father's second marriage to Yolande of Dreux, Queen of Scotland and attempted to contest its legality.
In 1297, John was married to his first wife Isabelle of Valois, eldest daughter of Charles of Valois and his first wife Marguerite of Anjou and Maine. Her maternal grandparents were Charles II of Naples and Maria Arpad of Hungary. At the time of their marriage John was eleven years old and his bride only five. Isabelle died childless in 1309.
In 1310, John married his second wife Isabella of Castile, daughter of Sancho IV of Castile and his wife María de Molina. John was twenty-four years old and Isabella twenty-seven. Isabella died childless in 1328.
In 1329, John married his third wife Joan of Savoy, the only child of Edward, Count of Savoy and Blanche of Burgundy. Her maternal grandparents were Robert II, Duke of Burgundy and Agnes of France, Duchess of Burgundy. John was forty-three years old and Joan about nineteen.
He predeceased his third wife by three years and died childless. He was unwilling to cede the Duchy to his half-brother, John of Montfort, son of his hated step-mother Yolande. He wished to leave the Duchy to the French king, 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 de Montfort claimed his rights as Duke, but the French King supported the Blois faction, and in turn the Breton War of Succession (1341–1364) was triggered. This Breton Civil War was fought between the House of Blois and the House of Montfort. This civil war became part of the Hundred Years' War, as England supported the Montfort faction, which won, against the House of Blois, which was supported by the France.