In the letter, he wrote: "As more time passes to your royal wedding, it becomes very clear that this is the biggest mistake in royal wedding history. I can understand it's awkward for Kensington Palace", she said on a British talk show, Loose Women.
And now his father has claimed that the stress of the open letter played a part in his health issues, when speaking to the US publication. Harry has since cleaned up his act, becoming one of the best-loved royals of the bunch, but perhaps he hasn't entirely shaken off his wild side.
Ever since Meghan and Prince Harry annouced their engagement, the bride-to-be has faced enough flak from her family, including her half sister, half brother and sister-in-law have all appeared on national television to criticise the American TV actress calling her names and claiming that she is a horrible person.
Meghan Markle, right, watches the closing ceremony of the Invictus Games with her mother Doria Ragland in Toronto, Canada, last year.
Mr Markle said: "It would have been better for the palace to have guided him, as well as us for that matter, to ensure the focus is on Harry and Meg and not her family back in the States".
Royal wedding 2018: Princess Charlotte to be bridesmaid
Thomas Markle, 73, is a retired Hollywood cinematographer who lives in Mexico and is divorced from Markle's mother. This is where we are expecting to see our first kiss.
Which way will Meghan and Harry go with their vows? Various sources have reported the guest list includes some 600 possible attendees and everyone's wondering if their fave made the cut. If it's handed to you, you take it. You don't shy away from it.
The seven-year old twins are Ivy's elder brothers and the whole family became close to Meghan whilst she was living in Canada and filming the television series "Suits".
Just after 1pm local time the couple's 25-minute carriage ride through the town in the Ascot Landau begins, with military representatives, and cheering crowds, lining the streets.
"I'm just so excited that the world will get to experience her loveliness, and I really think that with her platform for charity and her fortitude - she's going to have a great moment to change the world".
Meanwhile on Wednesday, her half-sister, Samantha Markle, was reportedly injured following a 'paparazzi confrontation' in Florida.