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Samantha Markle, Meghan's half-sister, has once again lashed out at her royal sibling for her "cold" behavior toward their father, Thomas, and said that it is on her if he dies.

On Tuesday, Markle went off on her duchess half-sister on Twitter calling her out for spending the day paying tribute to Nelson Mandela and his family but not taking the time to talk to her own.

"How about you pay tribute to your own father?!" Markle wrote in one tweet. "Enough is enough. Act like a humanitarian, act like a woman. If our father dies, it's on you Meg!"

Tagging Kensington Palace in her series of tweets, the 53-year-old continued, "Glad you have so much time to gallivant around paying tribute to others while ignoring your own father! How cold can you be and look in the mirror? Harry? I guess I was right."

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The Duke and Duchess of Sussex were snapped while pay tribute to the Nelson Mandela exhibition in London on Tuesday. (AP)

The tweets came just after Thomas Markle revealed to TMZ that he wasn't going to stop talking and was "unfazed" by reports that Prince Harry and his daughter were "frustrated" with his recent interviews with both The Sun and the British morning show "Good Morning Britain." But despite what Meghan's half-sister calls another family feud which Meghan is "responsible" for, their dad said that he still wants nothing more than to be a part of his daughter's life.

"I was silent for a full year and the press beat me up every day saying I was a hermit hiding in Mexico, so I gave my story," Thomas Markle said to TMZ, referring to his first TV interview.

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Thomas Markle said he believes his daughter is "terrified" adjusting her life as the Duchess of Sussex. (Mega/Reuters)

In his most recent interview with The Sun, he said his daughter seemed "terrified" while on public outings with her new husband.

"Apparently that interview put the Royal Family in their silence mode ... so, I gave another interview to break the silence. All they have to do is speak to me.”

He then added, "I’m enjoying the fact that I can make the entire royal family not speak and maybe I can get a laugh out of the duchess."

Samantha Markle continued to defend her father in a final tweet which read, "My father is not an embarrassment for loving his daughter! The Royals are an embarrassment for being so cold. You should be ashamed of yourselves."