So have any of you stumbled upon the story of Captain Philippe d'Orléans, comte de Paris? He was the grandson of the last ruling king in France, Louis-Philippe (the one who transformed into a pear) and became the next in line for the house of Orléans.
During the years of Napoleon III, he went into exile in the United States, along with his uncle and brother. At the outbreak of the war, he offered his services (along with his brother) to the Union and received a commission as one of McClellan staff officers. He served through Peninsular Campaign until resigning his commission in July of 62. He spent the rest of the war in the north as a writer, and published a comprehensive French language history of the American Civil War. (I just discovered the BNF has digitized the whole thing, so I am diving in on my kindle.)
After the war and the fall of Napoleon III, he was a leading contender to be made King in a restoration. On the death of the Comte de Chambord (who was almost made King...but he refused to take the crown if France didn't ditch the Tri-color and go back to the old royal flag! :bonk in 1883, his supporters styled him King Philippe VII, but by that point the French had rethought the whole king thing, and decided to stay a republic.
Small world the 19th century...