Harry and Meghan have been estranged from the British royal family since stepping away from official duties in 2020 and moving to California, but continue to attract huge interest both in Britain and abroad.
In extracts from his new book published in the Times newspaper, author Tom Bower, who has written a number of biographies about the royals, said the couple began feuding with the other royals shortly after their glittering 2018 wedding.
The couple are now barely on speaking terms with the other royals and Harry has rarely seen his father King Charles in recent years.
Bower wrote that the Prince and Princess of Wales were alarmed by Meghan's impact on him and regarded her as a threat.
"Meghan's brainwashed Harry," Camilla told a friend, according to the author.
According to the extracts, Harry was also shocked by the fall from grace of his uncle Andrew Mountbatten-Windsor, who has lost all his titles and been ejected from his home over his links to the late convicted US sex offender Jeffrey Epstein, and feared his brother would likewise effectively banish him.
In an unusually strong response, a spokesperson for Harry and Meghan said Bower's commentary had "long crossed the line from criticism into fixation".
"Those interested in facts will look elsewhere; those seeking deranged conspiracy and melodrama know exactly where to find him," the spokesperson said in a statement on Saturday.
Buckingham Palace declined to comment on behalf of King Charles and Queen Camilla.
There was no immediate comment from representatives of the Prince William and his wife Kate.
