Royal author Tom Bower claimed in his new book that the explosive altercation took place during the annual Commonwealth Day Service at Westminster Abbey in 2020.
Harry and Meghan attended the event to celebrate their latest engagement as senior royals.
The Queen, Prince Charles, Kate, Duchess of Cambridge and Prince William also attended the event.
Bower’s book, Revenge: Meghan, Harry and the War between the Windsors, spoke of the service, claiming that a “monumental brawl” took place during the day.
He said it happened after “Palace officials… decided to publicly humiliate” [Harry and Meghan]”.
“In the end, to end the dispute, William and Kate agreed that they would also wait with Harry and Meghan. When the members of the royal family entered the abbey, the shaky relations could not be hidden.
‘Kate had silenced the Sussexes and William’s greeting was cold. Harry looked tense. Meghan’s face showed bewilderment.’
Bower has made some explosive claims about the Duchess, including that she married Harry to become famous.
During an interview on Good Morning Britain, he claimed that once Meghan realized the royal family was “a lot of work and little pay”, she stopped liking it.
He said, “It’s wrong to say she was a famous actress, she wasn’t, she was a third-rate actress.”
Host Ben Shephard hit back at his comments, saying, “She was a very famous actress. She had a high profile in Hollywood and Suits is a series that was streamed all over the world so people knew who she was.”
Mr Bower replied, “Well, we won’t argue, but I don’t agree with you.”