Louis XVII (1781 - 1805?) was King of France during the Trans-Oceanic War, initially under a regency headed by his mother, Marie Antoinette. During the regency, Louis's mother formed an alliance with her nephew, the Emperor Francis II of Austria. Together, the two launched the Trans-Oceanic War in April 1795 by invading Prussia. Great Britain entered the war when France's Spanish ally threatened to invade Portugal, and by 1798 the combined British and Prussian armies had defeated the Spanish, French, and Austrian forces. Popular discontent with the war led to a revolt in Paris in the early months of 1799, which was put down by British and Prussian troops. The victorious allied troops continued to occupy Paris for several years after the signing of the Treaty of Aix-la-Chapelle in March 1799, and Louis remained little more than an Anglo-German puppet for the remainder of his reign.
Sobel does not state when Louis died, but the subtitle of his source for the King's later years, Charles Agissiz' The King on a String: The Last Years of Louis XVII (London, 1956), suggests that Louis did not long survive his country's defeat.
IOW, Louis died at age 7 in 1789, and never succeeded to the French throne.