Louis XIX was the King of France in the mid-1850s. After an armistice ended fighting in the Rocky Mountain War, Mexican President Hector Niles approached Louis seeking long-term loans to aid the United States of Mexico in recovering from the war. Louis considered the U.S.M. his protégé, and he was willing to cooperate. By 1858, French loans helped to raise the U.S.M. to its pre-war economic level.
Sobel does not mention Louis' family relationship to any other French monarchs in the nineteenth century. It is possible that Louis was a cousin of Henry V who succeeded to the French throne after Henry died without a male heir. It seems likely that Louis was the father of Louis XX, who abdicated in December 1879.