After this, he was persistently disloyal to the King, conspiring with Charles, Count of Charolais, and with Edward IV of England+, his nephew by marriage. The final treason came in 1474 when Saint-Pol approached Charles the Bold+, Duke of Burgundy+, who had already entered into a compact with Edward IV of England to dismember France in a renewal of the Hundred Years' War. The scheme envisaged the murder of Louis and the sub-division of France between Saint-Pol, the Dukes of Burgundy, Brittany, Bourbon and Namours, the Count of Maine+ and King Edward. Saint-Pol then proceeded to draw other magnates into the conspiracy.
The whole thing started to unravel after Louis and Edward concluded the Treaty of Picquigny+ in August 1475. Angered by this, Saint-Pol was imprudent enough to write to Edward, upbraiding him as a "cowardly, dishonoured and beggarly king". Edward promptly forwarded the letter to Louis, who now had all the proof he needed. A messenger was sent to the conspirator, in which he was informed that the King had 'need of a head such as his.' He was arrested in September 1475, and later imprisoned in the Bastille+. Execution followed in December. Philippe de Commynes+, the chief chronicler of Louis' reign, was to write that Saint-Pol had been "abandoned by God because he had tried with all his might to prolong the hostilities between the King and the Duke of Burgunday."
Louis de Luxembourg, Count of Saint-Pol+ Louis de Luxembourg, Count of Saint-Pol, of Brienne, de Ligny, and Conversano (1418 – 19 December 1475) belonged to the Ligny branch of the House of Luxemburg and was Constable of France.