Charles V., encouraged by his successes, determined to take part likewise in that which was still going on between the two claimants to the duchy of Brittany, Charles of Blois and John of Montfort.

Du Guesclin was sent to support Charles of Blois; "whereat he was greatly rejoiced," says Froissart, "for he had always held the said lord Charles for his rightful lord." The Count and Countess of Blois "received him right joyously and pleasantly, and the best part of the barons of Brittany likewise had lord Charles of Blois in regard and affection." Du Guesclin entered at once on the campaign, and marched upon Auray, which was being besieged by the Count of Montfort.
But there he was destined to encounter the most formidable of his adversaries.

John of Montfort had claimed the support of his patron, the king of England, and John Chandos, the most famous of the English commanders, had applied to the Prince of Wales to know what he was to do.
"You may go full well," the prince had answered, "since the French are going for the Count of Blois; I give you good leave." Chandos, delighted, set hastily to work recruiting.

Only a few Aquitanians decided to join him, for they were beginning to be disgusted with English rule, and the French national spirit was developing itself throughout Gascony, even in the Prince of Wales's immediate circle.

Chandos recruited scarcely any but English or Bretons, and when, to the great joy of the Count of Montfort, he arrived before Auray, "he brought," says Froissart, "full sixteen hundred fighting men, knights, and squires, English and Breton, and about eight or nine hundred archers." Du Guesclin's troops were pretty nearly equal in number, and not less brave, but less well disciplined, and probably also less ably commanded.