Lady Colin Campbell, known as Lady C, claims Meghan Markle should not write a memoir because "everybody's so turned off by them [the Sussexes] and their constant antics and lies."
It follows reports that Prince Harry could be writing a sequel to his own biography, Spare.
In his new book, named Charles III: New King, New Court, The Inside Story, which is currently being serialised in the Mail, Robert Hardman wrote: "The most concerning thing about the book for the Palace was the concealment of significant portions of more recent occurrences.
"It did not go unnoticed that Harry and Meghan’s wedding, their married life, and their eventual departure from the royal world amounted to a small part – less than a fifth – of Prince Harry’s memoir. This suggested either a sequel or, perhaps a memoir by Meghan in due course."
Harry and Meghan were slammed by Lady C
GettySpeaking to GB News, Lady C said: "I have been told that Meghan is the one who is going to be writing a book and that Omid Scobie set up the situation for her to name the King and the Princess of Wales.
"The book is not going to be written by Harry, it's going to be written by Meghan. But the fact of the matter is, in my opinion, everybody's so turned off by them and their constant antics and lies.
"I don't think people are going to buy the book, in the same way that nobody has bought Endgame.
"It has tanked most appallingly. I suspect any book she writes is going to tank as well. And if it doesn't, her reputation will be sucked. She's going to tank with it."
Harry already released his memoir called Spare
ReutersRoyal journalist Phil Dampier agreed with Lady C and said: "We've had Finding Freedom, we've had Endgame which were both written by Scobie and we've also had Spare.
"Now he left quite a few chunks out of Spare, things that he could talk about. It might well be done by Meghan.
"This is something that's been hanging over the Royal Family and is probably one of the main barriers to any kind of reconciliation.
"Because the King and William and Kate will just be worried that anything they say, any communications, any phone calls will end up in a new book. That is the big problem. They just don't trust him."
Lady C blasted them and said: "her reputation will tank’
PAPrince Harry and Meghan Markle made headlines recently after it was revealed that the Hardman's book, claimed the Queen was "very angry" that the couple named their daughter after her childhood nickname, Lilibet.
Queen Elizabeth reportedly told Palace aides at the time: "I don't own the palaces or the paintings, only my name, and now they've taken that."
Scobie, who wrote the controversial royal biography Endgame at the end of last year, has taken a swipe at the claims in a social media post.
Scobie wrote on X: "None of these Lilibet 'revelations' are doing the late Queen Elizabeth II any favours."
GB News has approached Archewell for comment on the claims, to which they are yet to respond.