Charles was a major player at a critical juncture in the Hundred Years' War between France and England, repeatedly switching sides in order to further his own agenda.

Charles made no secret of his role in the murder, and within a few days was intriguing with the English for military support against his father-in-law King John II, whose favourite the Constable had been.

Once again, Charles changed sides: the threat of a renewed English invasion forced John to make a new agreement of reconciliation with him, which was ultimately sealed by the Treaty of Valognes on 10 September 1355.

There were also continued rumours of his plots against the king, and on 5 April 1356 John II and a group of supporters burst unannounced into the Dauphin's castle at Rouen, arrested Charles of Navarre and imprisoned him.

However, many of his partisans were active in the Estates General, which endeavoured to govern and reform France in the power vacuum created by the imprisonment of the king, while much of the country degenerated into anarchy.

Meanwhile his brother Philip of Navarre threw in his lot with the invading English army of the Duke of Lancaster, and made war on the Dauphin's forces throughout Normandy.

Charles demanded an indemnity for all damage done to his territories while he had been imprisoned, free pardon for all his crimes and those of his supporters, and honourable burial for his associates executed by John II at Rouen.

Charles meanwhile gave his executed followers a solemn state funeral in Rouen Cathedral on 10 January 1358 and effectively declared civil war, leading a combined Anglo-Navarrese force against the Dauphin's garrisons.

He could not resist the chance to appear as a leader of the French aristocracy and led the suppression of the Jacquerie at the Battle of Mello, 10 June 1358 and the subsequent massacres of rebels.

Before long there were anti-English riots in the city and Charles, with Etienne Marcel, was forced by the mob to lead them against the marauding garrisons to the north and west of the city—against his own men.

After protracted haggling the two leaders met near Pontoise on 19 August 1359; on the second day Charles of Navarre publicly renounced all his demands for territory and money, saying he wanted nothing more than what he had at the beginning of hostilities and 'wanted nothing more than to do his duty to his country'.

John II had died in England in April, and news of the victory of Cocherel reached the Dauphin on 18 May at Rheims, where on the following day he was crowned Charles V of France.

Meanwhile Charles's brother Louis of Navarre led an army augmented by contingents pledged by the captains of the Great Company and the freebooter Seguin de Badefol through the Black Prince's territories and across France, evading the French royal forces sent to intercept him and arrived in Normandy on 23 September.

Hearing of the collapse of the civil war in Brittany after the Battle of Auray on 29 September, Louis abandoned his design to invade Burgundy and instead set about reconquering the Cotentin for Charles.

Although Charles offered Bernard-Aiz V, Lord of Albret, huge sums to take over the command of his forces around Burgundy, he finally realized he could not prevail against the King of France and must come to an accommodation with him.

In May 1365, in Pamplona, he agreed to a treaty by which there was to be a general amnesty for his supporters, the remains of Navarrese executed and displayed for treason were to be returned to their families, prisoners would be mutually released without ransom.

At the end of 1365 Séguin de Badefol arrived in Navarre to claim the considerable sums Charles had pledged to pay him for his services in Burgundy, even though he had achieved nothing of substance.

He then reneged on his agreements to both sides and attempted to hold the Navarrese borders intact, but was unable to do so and instead paid the invaders a large sum to keep their plundering to a minimum.

After Henry of Trastámara successfully seized the throne of Castile, Pedro I fled to the court of the Black Prince in Aquitaine, who began to plot his restoration by sending an army across the Pyrenees.

In July 1366 Charles himself came to Bordeaux to consult with Pedro I and the Prince and agreed to keep the mountain passes of Navarre open for the passage of the army, for which he would be rewarded with the Castilian provinces of Guipúzcoa and Álava as well as additional fortresses and a large cash payment.

On the strength of Charles of Navarre's offers, Edward III despatched an expeditionary force to the Seine estuary under Sir Robert Knolles in July of 1370.

Though Edward III sealed a draft treaty with Navarre on 2 December 1370 it was a dead letter after the destruction of Knolles's army at the Battle of Pontvallain a few days later.

[29] Nevertheless in March 1374 Charles met John of Gaunt in Dax in Gascony and agreed to let him use Navarre as a base for invading Castile on condition he recapture the towns surrendered to Henry.

In order to placate the Castilian King he now agreed for his eldest son, the future Charles III of Navarre, to marry Henry of Trastámara's daughter Leonora in May 1375.

Instead he sent off his eldest son to Normandy, with a number of officials, including his chamberlain Jacques de Rue, who were to prepare his castles to receive the English, as well as a servant whose mission was to insinuate himself into the royal kitchens in Paris and poison the King of France.

The draft treaties and correspondence with the English found in their baggage, along with Jacques de Rue's confessions under interrogation, were all that Charles V needed to send an army into northern Normandy to capture all the King of Navarre's remaining domains there (April–June 1378).

Charles II retreated over the Pyrenees to Saint-Jean-Pied-de-Port and in October he made his way to Bordeaux to plead for military aid from Sir John Neville, the Lieutenant of Gascony.

He retained his crown and his country but he was effectively a humiliated client of his enemies, he had lost his French territories and his Pyrenean realm was devastated and impoverished by war.

This is Francis Blagdon's English account, of 1803: Charles the Bad, having fallen into such a state of decay that he could not make use of his limbs, consulted his physician, who ordered him to be wrapped up from head to foot, in a linen cloth impregnated with brandy, so that he might be inclosed [sic] in it to the very neck as in a sack.

He had enjoyed the benefit of this singular prescription some time in safety, but now, as he was perpetrating his barbarities on the representatives of his kingdom, "by the pleasure of God, or of the devil," says Froissart, "the fire caught to his sheets, and from that to his person, swathed as it was in matter highly inflammable."