The Titles of Nobility Amendment was a proposal to the Constitution by the 11th Congress in 1810. It was passed by Congress, but not ratified by enough states. It's currently pending as Congress imposed no time limit. It's text is as follows:
"If any citizen of the United States shall accept, claim, receive or retain, any title of nobility or honour, or shall, without the consent of Congress, accept and retain any present, pension, office or emolument of any kind whatever, from any emperor, king, prince or foreign power, such person shall cease to be a citizen of the United States, and shall be incapable of holding any office of trust or profit under them, or either of them."
It is thought that Congress enacted to pass this amendment to revoke citizenship of the child of Jérôme Bonaparte (younger brother of Napoleon Bonaparte), and his American wife Betsy Patterson.