When I came across an entry in the occupation database that listed one man's occupation as "prince" I thought it must be an error. I was wrong.

Captain Antoine Philippe (listed in LAC as PHILLIPPE, ANTOINE GASTON BRAGANZA) was the Prince of Orleans and Braganza. A former aide de camp to Brig-General Seely, Commander of the Canadian Cavalry Brigade, Captain Philippe was killed November 29 1918 in a plane crash (source needed) and buried in the Dreux Royal Chapel in France.

What was a French prince, the son of Prince Gaston of Bourbon-Orleans of Chateau D'Eu, Normandy, France, doing in the Canadian Military during World War I? He was prevented from joining the French forces by an old law that did not permit members of the deposed French Royal Family to serve in the military.

http://www.canadiangreatwarproject.com/searches/soldierDetail.asp?ID=60713