The British outlet also revealed Thomas' response, which touches on his heart attack (the reason he missed the wedding) and hints at a possible disagreement between him and Prince Harry.
"Daddy, it is with a heavy heart that I write this, not understanding why you have chosen to take this path, turning a blind eye to the pain you are causing", Meghan, 37, wrote in August 2018.
Meghan's letter to Thomas said that he had broken his heart "into a million pieces". I came by there one day, and she had ordered an incredible ice cream and sorbet stand for the office.
Sharing excerpts from the five-page handwritten letter with The Mail On Sunday, the former lighting director claims he kept the letter out of the public "out of respect to Meghan". I'm telling you I don't want to communicate through the media, and you're asking me to communicate through the media.
Until evidence proves us wrong, we'd like to believe the latter, that Meghan is in fact, not hard to work with and that her work ethic is just one that many are still acclimatising to or something along those lines.
She even described Samantha as "your (Thomas Markle) other daughter, who I barely know". However, Kensington Palace has not addressed the letter, and a royal insider says that the duchess has no plans to comment, fearing it could escalate an already hard situation.
Apparently, the Duchess also admonishes her father, in anguished tones, for siding with Samantha while she "silently suffered at the hand of her vicious lies".
It added, "If you love me, as you tell the press you do, please stop".
Mr Markle was countering media reports that he has not reached out to her after an unnamed friend of the duchess told United States magazine People: 'He's never called; he's never texted.
It's pretty damn heartbreaking to read a letter from a woman begging her father to stop exploiting her for fame and money. Please allow us to live our lives in peace.
To which, Samantha responded: "If I had 600 mil she would care".
Meghan begged her father to "stop creating so much pain". "I can't force you", he reportedly wrote. I'm human and I'm sorry!
"When I opened the letter I was hoping it was the olive branch I'd longed for", he said. He then asked for a photo opportunity: "I wish we could get together and take a photo for the whole world to see". If you and Harry don't like it? "Fake it for one photo".