Francis was the youngest of 13 children of Ferdinand Albert II, Duke of Brunswick-Wolfenbüttel and Antoinette Amalie (1696–1762); his sister Luise of Brunswick-Wolfenbüttel married Prince Augustus William of Prussia, brother of Frederick the Great.

[2] On 14 October 1758, the Austrians, commanded by Daun, surprised the Prussians with a pre-dawn assault on the sleeping camp.

This successful action initially repulsed the Austrian advance, giving Frederick hope that the situation could be won.

Even after Keith himself was shot and killed, Frederick still thought the battle could be retrieved and returned to the rear echelons to take command.

As Francis approached the village, Austrian cannon-fire sheared his head off his shoulders.