Jean IV. (De Montfort), duke of Brittanv, born in 1293, died in Ilennebon, Sept. 26, 1345. He was the son of Duke Arthur II., and succeeded his brother Jean III. in 1341. The latter had bequeathed the duchy to Charles of Blois, husband of his niece; but Montfort found little difficulty in getting possession, and Charles complained to the king, Philip of Va-lois, who sent an army to besiege the usurper in Nantes. In order to save the city from assault, Montfort surrendered and was carried prisoner to Paris; but in the mean time his wife, Jeanne of Flanders, put herself at the head of his partisans and withdrew to Henne-bon, where she defended herself against the forces of Charles, on one occasion repelling an assault at the head of 300 cavaliers. The arrival of auxiliaries sent by Edward III. of England, to whom Montfort had done homage for Brittany, obliged Charles to raise the siege. A second attempt upon the same city in 1342 was equally unsuccessful, and Charles soon lost successively Guerande, Vannes, Carhaix, and Quimperle. In the same year Edward III. arrived in France with fresh troops and advanced to Rennes, where Philip marched out to meet him. By the mediation of the pope a truce was concluded between the monarchs.

Mont-fort's party, which before was barely a match for his rival's, had grown during his imprisonment. He escaped in disguise in 1345, and went to England, whence he returned with troops and made an unsuccessful attempt upon Quimper. He then retired to Hennebon, where he died a few weeks afterward, leaving a son who continued the war with Charles, and became duke as Jean V.