“My book deals with my bi-racial family in a candid, warm, personal and socially important way,” the 51-year-old told The Daily Star.
“Maybe when Meghan is more mature and reads the book she’ll understand. Some of it she won’t like, some of it she might,” she added.
Hmm, a bit of bad blood there perhaps?
The British publication revealed that the current working title is The Diary of Princess Pushy’s Sister.
“It’s not a threat, it’s a fact and a good book. Just wait and see,” Samantha tweeted following the shock announcement.
Samantha, who suffers from multiple sclerosis and is wheelchair bound as a result, and Meghan both have the same father - Tom Markle.
The mother-of-three, who claims to have helped raise Meghan, believes her sibling has always had royal ambitions, musing, “Her behaviour is certainly not befitting of a Royal Family member," before adding she was driven by “social climbing."
“Hollywood has changed her. I think her ambition is to become a princess.”
“It was something she dreamed of as a girl when we watched the royals on TV. She always preferred Prince Harry — she has a soft spot for gingers.”
The pair have not been on speaking terms since 2008.
Samantha's mother, Roslyn, has spoken out about the 51-year-old, simply saying, "Everything she has said about her is a lie."
Despite Samantha's controversial comments about her little sister, the former model does have fond memories of Meghan.
"She's not wild, she's not garish, she's not a partier," Sam told Entertainment Tonight.
"She's just very beautiful and conservative, very real, very giving. She's just a peaceful person."
Meanwhile, Meghan spoke of her family through a column in Elle UK.
"My parents came from little so they made a choice to give a lot: buying turkeys for homeless shelters at Thanksgiving, delivering meals to people in hospices, giving spare change to those asking for it," the 35-year reflected.
"It's what I grew up seeing, so it's what I grew up being: a young adult with a social consciousness to do what I could and speak up when I knew something was wrong."