 Francesco fought at the Battle of Bicocca, on the side of the emperor, in 1522.In 1526 he switched sides, joining the League of Cognac, together with Francis I of France, Pope Clement VII and the Republic of Florence, and was besieged in the Castello Sforzesco.On May 4, 1534 he married the 12-year-old niece of Charles V, Christina of Denmark, the daughter of Christian II of Denmark and Isabella of Burgundy.