A royal biographer is weighing in on the allegations that Prince William cheated on Kate Middleton with his wife's former friend, Rose Hanbury.

The affair rumors once again became a topic of discussion this week after they were discussed in royal author and correspondent Omid Scobie's new book, "Endgame: Inside the Royal Family and the Monarchy's Fight for Survival."

In an exclusive interview with Entertainment Tonight, Scobie dismissed the allegation, emphasizing that it was merely a rumor without substantial evidence.

But he said he wasn't surprised by how fast the rumor spread, stating, "Unfortunately, if a rumor's left to kind of do its own thing it can run 20 laps around the world before you even think about what, how you want to kind of address it."

The affair speculation first surfaced in 2019 following a report in a U.K. tabloid, according to ET. They were fueled by Middleton seemingly avoiding Prince William's PDA during an outing around the time the allegations began circulating.

Rose Hanbury
(Photo : Getty Images/Victoria Jones- WPA Pool)
Rose Hanbury (L) arrives through the East Gallery for a State Banquet at Buckingham Palace on June 3, 2019 in London, England.

The royal expert acknowledged the sensitivity of the topic, given its potential impact on the reputation of Prince William and his marriage with Princess Kate.

Scobie noted that he was "very careful" about the way he discussed the allegations and the couple's alleged "fallout" with Hanbury in his book.

"For legal reasons, there are so many things that one can't go into, but I thought it was really important, even if a rumor is a rumor. And I really don't see proof that there is more to this than just a tittle-tattle, you know," he added.

Despite stating there's no truth to the rumors, Scobie claimed that the palace indirectly addressed the matter by diverting attention to Prince Harry and Meghan Markle, who stepped back from their roles as senior working royals in early 2020.

"I thought it was really interesting to analyze how the palace dealt with that," Scobie told the outlet, highlighting the palace's concern about the negative impact on William's reputation.

Scobie's book has been drawing controversy since it was released earlier this week.

The controversy escalated when a Dutch translation unintentionally revealed the names of two royals who allegedly expressed concerns about the skin color of Prince Harry and Meghan Markle's son, Archie.

Scobie claimed the royals were named in private letters exchanged between King Charles and Markle but maintained that he did not identify the royals in his English manuscript because of libel laws.

The Dutch version was withdrawn from shelves due to the error, and the publisher plans to rerelease the book after rectifying the issue.

Piers Morgan intensified the media storm by controversially naming King Charles III and Princess Kate on his show as the royals mentioned in the Dutch copies of Scobie's book.

The Telegraph reported that Buckingham Palace is considering legal action following Morgan's move, with an unnamed royal source telling the outlet, "We are considering all options."