I may come across as rather pompous Gromit but what the hell here is my slant on things.
Prince Harry is not only a Prince of the Realm, but he is also an Officer and a Gentleman, and his regiment is the Blues and Royals, part of the Household Cavalry.
With all this in mind he should be expected to behave in such a way as not to bring disgrace upon his family, his Rank or his Regiment.
The secret is not to be found out, but being who he is, this would be almost impossible.