Prince Harry has said he is considering applying for American citizenship. He has lived in Montecito, California for four years now.
If he were to make this request, the prince could be forced to renounce his titles of nobility. This is something that, theoretically, could go all the way to the Supreme Court, because they would have to review the law to make sure it is constitutional. But there is no Supreme Court decision that interprets this section of the code, simply because there have only been about a dozen American citizens holding a title of prince or princess in history.