Despite his record of defeats, he was able to retain his position. He was able to attain command ahead of the more popular Marshal Browne because of the support of his brother who had significant influence over military appointments. During Austria's Third Silesian War against Prussia, he commanded the army of the Roman-German Emperor at the Battle of Prague, where he was again defeated by Frederick the Great, king of Prussia, but was able to inflict heavy casualties on the larger Prussian forces. He subsequently defeated a smaller Prussian army in 1757 at the Battle of Breslau before being completely routed by Frederick the Great at the Battle of Leuthen, which is considered one of Frederick's most brilliant victories. During the battle, he was commander of the Imperial Army as appointed by Maria Theresa. At Leuthen, the Austrians were overwhelmingly defeated by an army half their size, with fewer guns, and tired after a long march over 12 days. Charles and his second in command, Count Leopold Joseph von Daun, sank "in the depths of despondency", and the Prince could not fathom what had happened. Charles had a mixed record against Frederick in past encounters but had never fared so badly as at Leuthen. After this crushing defeat, Maria Theresa replaced him with Daun; Charles retired from military service and subsequently served as the governor of the Habsburg Netherlands. Though an unsuccessful military leader, Charles proved to be a competent administrator, well-liked by the population. Under him, the Austrian Netherlands flourished, and he was deeply involved in the cultural life of his province.
Family and private life
Because Charles ruled by right of his marriage to Maria Anna of Austria, Maria Anna's death very shortly after marriage created a situation where his mistress Elisabeth de Vaux, other mistresses, and children, were kept under strict privacy and not made public; indeed, his children were to present themselves only under the surnames of their mothers while in public so long as they were in the Netherlands. Though there is obscurity about his private affairs after the death of Maria Anna, it is known that from his mistress Elisabeth de Vaux, Charles had a son Charles Alexandre Guillaume Joseph, and a grandson through the same; a stillborn daughter by an unnamed mistress; a son Charles Frédéric by an unnamed mistress; a son Jean Nicholas and a daughter Anne Françoise by an unnamed mistress, and an unnamed daughter through a mistress named Regine von Porthenfeld. Some of his children were known to have lived in Dutch-speaking parts of Belgium temporarily or permanently, including his first son Charles Alexandre Guillaume Joseph, who was later known to have returned to Lunéville in Lorraine, to have claimed a substantially bountiful inheritance, to have had a son Gustav Auguste in 1788, and to have died in Nancy.