Two stars of the 1937 version, David Niven and Douglas Fairbanks Jr., took their swashbuckling to Real Life in World War II. Both served in elite units (Niven in the Commandos, Fairbanks in the U.S. Navy Beach Jumpers) both saw combat and both were highly decorated for their actions.
By this point in his career, Ronald Colman had played so many double roles that he was fed up with them (and had, in fact, refused to do so for A Tale of Two Cities). On the other hand, the King's role is tiny and Rudolf Rassendyll gets most of the action.
Reportedly Douglas Fairbanks, Jr. was extremely reluctant to play a villain, but after he allowed himself to be talked into it he turned in a bravura performance that literally makes the film.