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.
Harry and Meghan could become “irrelevant” like Edward and Wallis, royal expert says
Edward VIII abdicated in 1936 after less than a year as king to marry Wallis Simpson
“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.”
The Duke and Duchess of Sussex quit royal duties last year for a new life in America
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.
Harry and Meghan are now living in California
“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.
“Both of them married divorced American women.
“We all know that, but it goes much deeper than that.”
Source: EXPRESS CO UK