Louis , Dauphin of France ( 4 September 1729 -- 20 December 1765 ) was the only surviving son of King Louis XV of France and his wife , Queen Marie Leszczyńska .
Louis of France ( Louis Ferdinand ; 4 September 1729 -- 20 December 1765 ) was the only surviving son of King Louis XV of France and his wife , Marie Leszczyńska .