Meet Meghan Markle's half-sister Samantha Grant, who's making headlines for lashing out at Prince Harry

• Meghan Markle's half sister, Samantha Grant, has been very vocal about the future wife of Prince Harry.
• She plans to release a "tell-all book" about Markle and their childhood. 
• Here's everything we know so far about Grant and her relationship with the future princess.

Meghan Markle has been under a microscope since her engagement to Prince Harry. But in between style praise and wedding hype, Markle has made headlines thanks to tweets from her estranged half-sister.

Samantha Grant, who goes by the name Samantha Markle on social media, has been sharing plenty of opinions about the newest addition to the royal family. She has even promised to write a book "complete with facts and photos" about her half-sister and their home life during childhood. 

So who exactly is Samantha Grant, and how does she factor into Markle's family dynamic?

Grant and Markle share a father.

Grant, 53, and Markle, 36, are half-siblings. According to Evening Standard, Grant is the daughter of Thomas Markle Sr. and his first wife, Roslyn. Markle's mother is his second wife, Doria. 

Grant has spoken openly about Markle's mother, calling her "beautiful" as well as "greedy and awful." She also threatened to write "the truth" about Doria, before deciding against it.

Grant is very fond of their shared father, however, calling him "self-sacrificing" and defending him against media criticism on numerous occasions. 

It's a different story with Grant's brother, Tom Markle Jr., who she has called a "lowlife" and a "lying thief."

She has multiple sclerosis and uses a wheelchair. 

According to The Sun, Grant was diagnosed with multiple sclerosis in 2008, and has barely spoken to Markle since then. 

"I didn't feel a separation from her until I was in the wheelchair," Grant told the publication. "The more high profile she became, she never mentioned me."

Grant, a former actress, is passionate about handicap accessibility and previously set up a GoFundMe page to make her home wheelchair accessible.

She wants to write a tell-all titled "The Diary of Princess Pushy's Sister."

Despite the disparaging title, Grant apparently does not aim to tear Markle down. Rather, she hopes to discuss "bigoted underpinnings" in their family.

"My book deals with my bi-racial family in a candid, warm, personal, and socially important way," Grant told the Daily Star.

According to Page Six, Grant's pitch to publishers focused on this lense: "If only I could predict the media frenzy and racial slurs that would occur as a direct result of my beautiful baby sister possibly becoming the first bi-racial princess or duchess in royal history."

"Samantha has been dogging [Markle] for years," Grant's mother, who reportedly hasn't spoken to her daughter in years, told the Daily Star. "Everything she has said about her is a lie."

Though Grant often mentions her book on Twitter, she has not shared any details about when it will be released. 

In spite of her harsh words, Grant has praised both Markle and Prince Harry.

In an October interview with Good Morning Britain, Grant called Markle "strong, very worldly, very educated, very graceful."

She also praised Prince Harry for humanitarianism and "chivalry" in defending his fiancée against negative reactions to their engagement.

It seems that there is still much to be discovered about the future princess' half-sister. Only time (and her book) will tell.

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