Charles II, 8th Duke of Bourbon, Count of Montpensier, known as the 'Constable of Bourbon', was a French nobleman who fought for both sides during the Italian Wars, after arguing with Francis I of France.
Charles was born into a minor branch of the Bourbon family, the son of Gilbert, comte de Montpensier. He owed his early fortune to the deaths of his father in 1496, his eldest brother in 1501 and his father's cousin Pierre II, duc de Bourbon, in 1503. Charles married Pierre's daughter and heir Suzanne, and by 1505 had thus inherited both the Montpensier estates and the property of the senior Bourbon line.
Bourbon entered the service of Louis XII of France. He fought at the siege of Genoa of 1507 and the battle of Agnadello of 1509.
He was appointed Constable of France in 1514 and kept that post under Francis I. In 1515 he commanded part of the French army at the battle of Marignano (War of the Holy League), and in 1516 Francis I appointed him Viceroy of Milan.
In 1523 Francis I made the mistake of demanding that Charles return the estates he had inherited from his wife after her death in 1521. This may have been a legally valid request (although the Parlement of Paris, where Francis was conducting the case, suspended judgement, suggesting that the case was bad), but it was politically stupid. The Parlement sequestered the property under question, making Francis I one of the trustees. Infuriated by this action, and warned by a failed attempt to arrest him, Charles entered the service of the Emperor Charles V. The original plan seems to have been for a division of France, with Bourbon getting the south and centre, and the English getting the crown, but the plotters delayed for too long and this plan was never put into effect.
Bourbon took part in the failed Imperial invasion of Provence in the summer of 1524, which stalled outside Marseilles. One aim of this invasion may well have been the division of France, but the idea didn't resurface again.
In 1524 Francis invaded Italy, and began a siege of Pavia (First Hapsburg-Valous War, 1521-26). The Emperor gave Bourbon command of the heavy cavalry in the army that was sent to lift the siege, and on 24 February 1525 he took part in the great Imperial victory of Pavia. Francis was captured at the battle and was taken to Spain, where in March 1526 he reluctantly agreed to the Treaty of Madrid, giving up his claims in Italy. One of the terms of the treaty was the restoration of Charles, and a guarantee that he could return to France.
The moment Francis was released he renounced the treaty on the grounds that he had signed it under duress (including the clauses related to Charles - Charles V made him Governor of Milan in compensation). This triggered the Second Hapsburg- Valois War (or War of the League of Cognac). Once again Bourbon was given command of the Imperial Army in Italy, and after capturing Milan in 1526 was sent south to attack Rome. In early May Bourbon ordered an assault on the walls, lacking the artillery to conduct a regular siege. Bourbon was killed early in the attack (6 May 1527), but his men still fought their way into the city. With no commander and its pay in arrears the Imperial army sacked Rome, a great embarrassment for Charles V, who saw himself as the defender of the Papacy.