He was forced to remain a year in England, in spite of the demands of Louis XV and the Emperor Charles VII. During the French campaigns of 1746–47, Belle-Isle was in command at the Alpine frontier. There his younger brother, the Chevalier de Belle-Isle, served under his command. The younger Belle-Isle led the French army sent to invade Piedmont where he was killed at the Battle of Assietta. Following the defeat, French forces were weakened and demoralized. However, the older Belle-Isle still managed to repel a follow-up invasion of the Provence by Austrian and Italian forces and pushed the fighting back into the plain of Lombardy. At the peace, having thus retrieved his military reputation from the disasters of 1742–43, Belle-Isle was made a Peer of France in 1748. King Louis XV would make him Secretary of State for War in 1758, a position Belle-Isle would hold until his death in 1761.