Meghan Markle's half-sister has mounted another verbal attack against her famous sibling, claiming she "doesn't have a heart" and has treated their father "coldly".
Ms Markle tells the show, due for broadcast on Friday: "She doesn't have a heart or she would have been doing everything she could to make him comfortable and reciprocate, and be loving, and gracious and make sure he's comfortable in his old age."
She also says in the documentary: "I pointed out that humanitarians don't treat their father coldly, was that a lie, no, because the world watched it happen to my dad and the world watched her do it."
It is understood in the months leading up to the duke and duchess' wedding both Meghan, now heavily pregnant, and Harry tried to build bridges with Thomas Markle.
But the relationship appears to have broken down after he allegedly mocked up paparazzi photographs of himself.
And it may be irrevocably damaged by his actions in February when Mr Markle made public a handwritten letter from his daughter penned last year.
In the personal note, the Duchess asked her father: "If you love me, as you tell the press you do, please stop. Please allow us to live our lives in peace."
Meghan also accused her father of breaking her heart "into a million pieces" by his actions.
Samantha was quick to brand the Duchess a "narcissist" for her emotional letter to her father, published earlier this month.
She also suggested Meghan might care about her if she had more money. “If I had 600 mil she would care,” she wrote.
Mr Markle, a former Hollywood lighting director who now lives in Mexico, has repeatedly told news outlets he has been shunned by his daughter and her husband.
Meghan And The Markles: A Family At War will air on Channel 5 on Friday.