The Duke of Sussex has been living in the U.S. for the past several months after he and his wife, Meghan Markle, stepped down from their roles in Britain's royal family. However, Queen Elizabeth allowed them to retain their titles and styles, on the condition that they don't use them when conducting business.
Now, royal expert Marlene Koenig is warning Harry that if he decides to become a U.S. citizen, he'll have to give up his title by default.
"He would literally have to, even though there is no law preventing him from still being called Prince Harry, but when you become a US citizen, you have to renounce any titles or allegiance," she said.
Specifically, the Constitution denounces royal titles within the first few pages, stating in Article 8 that "No title of nobility shall be granted by the United States," and then goes on to prohibit public office holders from being granted titles, or being given other benefits, from foreign heads of state.
Koenig noted that he could still unofficially refer to himself as "Prince Harry," since there is nothing stopping him from doing it. For example, she pointed to a hypothetical situation in which an American citizen tried to use a royal title in daily life.
"You might not put that on your business card if you're a carpenter but it's not against the law," she said.
She went on to note that there are at least two U.S. citizens who are "peers" with British titles. One of whom is the Earl of Wharncliffe. She was referring to Richard Wortley, who, according to a 1987 New York Times article, was living in Maine when he inherited the title following the death of a relative.
She also pointed to another time in history when the grandchild of a British monarch gave up their titles. In 1919, Queen Victoria's granddaughter, Princess Patricia of Connaught, voluntarily relinquished her titles, while at the same time maintaining a loose connection to the royal family.
"She didn't stop being a princess... She just wasn't styled," she said.
As for Harry, Koenig also noted that if he became an American citizen he would face a much more real and immediate problem than just his title: he would have to pay U.S. taxes.