King John was to be released and his son held as hostage until the enormous ransom was paid.

Of course the money could not be paid by impoverished France, for such a doubtful benefit, at least; and so the son and hostage made his escape.

Then King John, faithful to his chivalrous creed, returned to London and captivity, dying in 1364.
The dauphin, who had now become Charles V., came to the throne with the determination of restoring France to herself.

His attention had been drawn to the military talents of a Breton youth--Bertrand du Guesclin.
Poor, diminutive in stature, deformed, he had raised himself to military positions usually reserved as a reward for sons of nobles.

In the reopening of a war with England, which Charles was planning, du Guesclin was to be the sword and he the brain.
The Black Prince had gone to Spain to fight the battles of Peter the Cruel, in a civil war in which the Prince was involved by inheritance, and was levying taxes for this Castilian war upon his new subjects in Aquitaine.