Royal commentator Nick Bullen said it was "fascinating" to compare Harry and his great-great-uncle, who abdicated in 1936 after less than a year as king to marry an American divorcee. Mr Bullen said Edward and Wallis Simpson "eventually became irrelevant" and questioned if the same thing will happen to the Duke and Duchess of Sussex, who quit royal duties last year for a new life in America.

       The royal expert, co-founder and editor-in-chief of True Royalty TV, made the comments ahead of the release of documentary The Royals Revealed: Harry and Edward, Princes in Exile.

       Mr Bullen told Fox News: "Even though Harry wasn’t the king and he didn’t abdicate, he still has a major impact on the monarchy.

       "I think the biggest lesson – or warning – that this documentary shares is the fact that Edward and Wallis Simpsons faded slowly into obscurity.

       "They eventually became irrelevant.

       "Will the same happen to Harry and Meghan as Prince William’s children take to the world stage?

       "It may seem far from now, but it will happen.

       "What will happen to Harry and Meghan 10 years from now?

       "Will they be the same stars they are now? Some historians have suggested that this is unlikely."

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       Mr Bullen claimed Edward and Wallis "faded into obscurity" and were "slightly awkward guests at dinner parties in New York".

       He said: "The big lesson viewers will learn from this documentary is how the Duke and Duchess of Windsor sort of faded into obscurity and became bit players on the world stage.

       "They were slightly awkward guests at dinner parties in New York.

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       "It raises the question, how long will Harry and Meghan Markle’s value stay at such a high level?

       "I think this documentary is a window to a story that has happened before and what could occur again."

       Mr Bullen also highlighted similarities between Harry and Edward, who both married Americans, had rifts with their brothers and released their memoirs.

       The royal expert said: "It’s fascinating when you draw the parallels between the two.

       "Both of them married divorced American women.

       "We all know that, but it goes much deeper than that."