Meghan Markle “feels sick to her stomach” about half-sister Samantha Markle‘s upcoming book, but she “won’t act bothered or upset about [it] in public,” a source exclusively tells In Touch.

Despite the Duchess of Sussex’s fears, husband Prince Harry is “totally supporting Meghan and doesn’t believe a word that comes out of Samantha’s mouth.”

The 328-page long memoir titled The Diary of Princess Pushy’s Sister Part 1 is set to be released on January 17. Although the 56-year-old promised the book wouldn’t be a “slamming tell-all story,” Meghan may not be “comfortable” with some of the things she penned.

“I don’t know if she will be comfortable with it. Some things she will and some things she won’t,” Samantha told U.K.’s The Sun. “It’s fair and balanced. Naturally, some things she will like and some things she won’t. Truth is stranger than fiction, and I have predicated myself on the truth.”

Prince Harry Meghan Markle Wedding
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In a separate interview with Us Weekly, the author clarified that her memoir “has never been designed to attack my sister,” she told the outlet. “It’s relatable. There’s a lot to learn — the good, the bad and the ugly. I’ve been very forthcoming that I was never writing a hardbound tabloid. I said that two years ago, but nobody wanted to believe it.”

Samantha first announced she would release a memoir in April 2017, more than one year before Meghan and Harry tied the knot in Windsor. The book, published by Barnes and Noble, has the synopsis: “Amidst a firestorm of fake news and media mayhem, Samantha Markle shares the truth about her life and family against all odds and ultimatums, as a royal fairytale plummets from the tea towels.”

Meghan and Samantha are related through their father, Thomas Markle Sr. Over the years, Samantha has been a vocal critic of Meghan.

In November 2016, she branded the then-star Suits a “social climber.” In April 2018, just one month before the royal wedding, Samantha attacked the couple for not inviting any member of the Markle family.

She wrote on Twitter, “Out of respect and humanitarianism, the Markles should be invited if 2,000 complete strangers are. Our uncle, brother, me, best friend of 30 years, nephews. Our issue is not a matter of closeness. Family is family.”

Following the birth of her nephew, Archie Harrison, in May 2019, Samantha told  DailyMail TV, “We’re all welcoming the baby — Markles, Raglands, Sussexes, Windsors. In terms of the gene pool, we’ve all made a contribution to this wonderful little boy who will probably grow up to be an exceptional man and we’d like to treat this as if we’re all a big family.”

Though she has not spoken to Meghan since 2008, she appears to want to make amends. “We’ve extended the olive branch,” Samantha told the Daily Mail, “and now it is Meghan’s turn.”

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