And when she had labored with them of France, she went her way to them of the Empire, to the Duke of Brabant, to the Marquis of Juliers, and to my Lord John of Hainault, and prayed them, for God's and pity's sake, that they would be pleased to hearken to some terms of accord, and would win over the King of England to be pleased to condescend thereto." In concert with the envoys of Pope Benedict XII., Joan of Valois at last succeeded in bringing the two sovereigns and their allies to a truce, which was concluded on the 25th of September, 1340, at first for nine months, and was afterwards renewed on several occasions up to the month of June, 1342.

Neither sovereign, and none of their allies, gave up anything, or bound themselves to anything more than not to fight during that interval; but they were, on both sides, without the power of carrying on without pause a struggle which they would not entirely abandon.
An unexpected incident led to its recommencement in spite of the truce: not, however, throughout France or directly between the two kings, but with fiery fierceness, though it was limited to a single province, and arose not in the name of the kingship of France, but out of a purely provincial question.

John III., Duke of Brittany and a faithful vassal of Philip of Valois, whom he had gone to support at Tournay "more stoutly and substantially than any of the other princes," says Froissart, died suddenly at Caen, on the 30th of April, 1341, on returning to his domain.
Though he had been thrice married, he left no child.

The duchy of Brittany then reverted to his brothers or their posterity , but his very next brother, Guy, Count of Penthievre, had been dead six years, and had left only a daughter, Joan, called the Cripple, married to Charles of Blois, nephew of the King of France.

The third brother was still alive; he too was named John, had from his mother the title of Count of Montfort, and claimed to be heir to the duchy of Brittany in preference to his niece Joan.