After the return of Maximilian, Philip actively participated in the suppression of the revolt of the Flemish cities (Ypres, Bruges and Ghent). When Maximilian was taken prisoner in Bruges, Philip volunteered to take his place as hostage, so that Maximilian could be released on May 16, 1488 under the condition of granting more freedom to the cities. But, once released, Maximilian refused to honour the agreement. Deeply hurt by the betrayal of his Lord, Philip joined the rebellious cities and became their military commander. He tried to conclude an alliance with King Charles VIII of France, but received little military support. Other attempts to ally with the Dutch Hooks, Brabant or Liège led to nothing. He was forced to surrender his last stronghold, Sluis, on 12 October 1492. In his allegory the "Weisskunig", Maximilian would later claim that the "blue king" bought Philip away; Koenigsberger argues that the Cleves family had "hovered for years" in its loyalties and Philip's switching sides "cannot therefore have come as a complete surprise to his contemporaries".