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Burgundy was left without a ruler in November 1361, and was claimed by
Charles; but, lacking both allies and money, he was unable to prevent
the French king from seizing Burgundy, while he himself returned to
Navarre.

In his own kingdom Charles took some steps to reform the financial and
judicial administration and so to increase his revenue; but he was soon
occupied once more with foreign entanglements, and in July 1362, in
alliance with Peter the Cruel, king of Castile, he invaded Aragon,
deserting his new ally soon afterwards for Peter IV., king of Aragon.
Meanwhile the war with the dauphin had been renewed. Still hankering
after Burgundy, Charles saw his French estates again seized; but after
some desultory warfare, chiefly in Normandy, peace was made in March
1365, and he returned to his work of interference in the politics of the
Spanish kingdoms. In turn he made treaties with the kings of Castile and
Aragon, who were at war with each other; promising to assist Peter the
Cruel to regain his throne, from which he had been driven in 1366 by his
half-brother Henry of Trastamara, and then assuring Henry and his ally
Peter of Aragon that he would aid them to retain Castile. He continued
this treacherous policy when Edward the Black Prince advanced to succour
Peter the Cruel; then signed a treaty with Edward of England, and then
in 1371 allied himself with Charles V. of France. His next important
move was to offer his assistance to Richard II. of England for an attack
upon France. About this time serious charges were brought against him.
Accused of attempting to poison the king of France and other prominent
persons, and of other crimes, his French estates were seized by order of
Charles V., and soon afterwards Navarre was invaded by the Castilians.
Won over by the surrender of Cherbourg in July 1378, the English under
John of Gaunt, duke of Lancaster, came to his aid; but a heavy price had
to be paid for the neutrality of the king of Castile. After the death of
Charles V. in 1380, the king of Navarre did not interfere in the
internal affairs of France, although he endeavoured vainly again to
obtain aid from Richard II., and to regain Cherbourg. His lands in
France were handed over to his eldest son Charles, who governed them
with the consent of the new king Charles VI. Charles died on the 1st of
January 1387, and many stories are current regarding the manner of his
death. Froissart relates that he was burned to death