Meghan Markle's estranged half-sister Samantha Grant is writing a tell-all book about their family that might show the "Suits" actress in a bad light.

Grant, 51, is set to publish a tell-all memoir that details what it is like to grow up with Markle. Speaking with Daily Star, Grant said her book explores the story of her bi-racial family in a "candid, warm, personal and socially important way." The book will also include details on her relationship with Markle, who might not like what Grant will reveal about her. "Maybe when Meghan is more mature and reads the book she'll understand," Grant stated. "Some of it she won't like, some of it she might."

The memoir's working title is "The Diary of Princess Pushy's Sister." Grant went on to criticize her half-sister by saying that Markle has always desired to be a princess but her attitude "is certainly not befitting of a royal family member."

Meanwhile, Grant's motives for penning the memoir might not be as innocent as they appear to be. Markle and Grant shared the same father, but they grew up with completely separate lives. A source recently told E! News that Markle has never had a relationship with her half-sister, who is now wheelchair bound due to multiple sclerosis.

"Samantha Grant doesn't have a relationship with Meghan Markle and she never has," the insider said. "As they were 17 years apart, they were never raised in the same house. Meghan was raised an only child by her loving parents."

Rumor has it that Markle will soon be engaged to her boyfriend Prince Harry, leading the source to believe that Grant might just be taking "advantage" of the TV star. Grant has also recently changed her last name to Markle — which the source claims as an effort by Grant to get to know the UN Women's advocate.

"If she hates Meghan so much, why is she suddenly trying to share an identity with her?" the source added.

Markle has yet to comment on the issue.