 Still a child, he was named in 1536 "Gran Camerlengo" of the Kingdom of Naples.At the head of the Spanish army in Lombardy and Piedmont since December 1555, he achieved an advantageous truce with France in March 1556, concluding the successful campaign started by the Duke of Alba.He was then Governor of the Duchy of Milan (1560–63) and viceroy of Sicily (1568–71), where he diminished the power of the local barons and the Deputation.