After the battle, François was taken to the Castle of Pizighettone near Cremona, where he remained for three months in the custody of the Spanish captain. Captured companions accompanied him, including his childhood friend Anne de Montmorency (who would remain François's most trusted counselor and eventually rise to the most powerful political position in France). These men were eventually given safe-conducts that enabled them to travel back and forth between Italy and France to negotiate the king's release. François appointed his mother, Louise de Savoye, regent during his absence. Louise established her court at Lyons, near the Italian border, to facilitate communications with her son and the emperor.
If François and his mother had hoped that Charles would quickly release him for a cash ransom, they were mistaken. Charles presented a long list of demands that included paying Charles's debts to Henry VIII, abandoning French claims to Milan and Genoa, and most importantly, ceding the duchy of Burgundy. The emperor planned to seal the settlement through the marriage of his niece, Mary of Portugal, to the Dauphin. Although François appeared amenable to some of the terms, he refused to negotiate as long as he continued to be held prisoner. He forwarded Charles's terms to Louise, who rejected them outright.
Hoping to cut short negotiations made all the lengthier by the distance separating the two courts, François begged for a face-to-face meeting with Charles. In June, he was taken to Spain on a fleet of galleys decorated in his honor, given a royal welcome in Barcelona, then moved to Valencia. He asked that his sister Marguerite be given safe-conduct to negotiate a peace, that he be moved closer to the site of negotiations for easier consultation, and that a truce be declared while the talks were in progress. Charles agreed to all three requests, yet continued to avoid meeting with François in person.
When the French ambassadors met with Charles in Toledo, the emperor continued to dismiss any discussion of a ransom. He was willing to make some concessions in his original demands, but claimed there could be no lasting peace as long as Burgundy remained in French hands. France, however, refused to consider surrendering the region; in fact, François, now in Madrid, made a secret declaration to the French ambassadors that he would never surrender Burgundy freely and that, if forced to do so, his action would be null and void.
Charles almost lost his opportunity to profit from the situation when François nearly died in September from a combination of acute depression, anorexia and a nasal abscess. The French king ran a fever for twenty-three straight days and lapsed into a semi-coma after Charles did, finally, come to see him. Later in the month, the abscess burst and François unexpectedly recovered. Peace talks resumed, this time facilitated by Marguerite, who had arrived during her brother's illness, but were suspended once again when Charles found the proposals unacceptable.
By the end of the year, the strain of the king's absence was growing too great for the kingdom. Louise de Savoye decided to abandon Burgundy and convinced François to accept Charles's terms. On January 14, 1526, the parties signed the Treaty of Madrid. In return for his freedom, François ceded Burgundy and abandoned his claims to Italy. He also agreed to hand over his two oldest sons as hostages until the terms of the treaty were fulfilled. In return, he demanded the hand of Charles's sister Eléonore in marriage, in order to keep her from marrying Charles de Bourbon, the prince of the blood who had sided with Charles during the war. Charles, swayed by advisors who believed the French king could be trusted, agreed. Little did he know that two days before the French king signed the treaty, he had made another secret declaration nullifying the surrender of Burgundy.
Betrothed by proxy to Eléonore in January, François remained in Madrid until mid-February, possibly for health reasons. Charles arrived, and together they traveled to meet Eléonore. A few days later, Charles set off to Seville to marry Isabella of Portugal, and François began the long journey back to France with his Spanish escort. The heartrending exchange of the monarch for his two young sons, which deserves a post of its own, was set for March 17 on the river Bidassoa.
[Source: The material for this post was condensed from R. J. Knecht's account in Renaissance Warrior and Patron, pp. 216-48.]