Markle's lawsuit against the outlet -- and their publishers, Associated Newspapers Limited -- was first filed last October, and is a result of the publication printing excerpts from a correspondence between herself and her estranged father, Thomas Markle.
A source close to the Sussexes tells ET, "The case centers on a private and hand-written letter from a daughter to her father that was published by The Mail on Sunday. This gross violation of any person's right to privacy is obvious and unlawful.” The source further stated that "the Duchess’ rights were violated."
According to the latest court documents, obtained by ET, Markle opposed the Kensington Palace press team's "no comment" directive regarding the reports about Markle's contentious relationship with her family, and she wanted to speak out in her own defense.
The docs state that, amid her pregnancy, the Duchess "had become the subject of a large number of false and damaging articles by the UK tabloid media, specifically by the Defendant [Associated Newspapers Limited], which caused tremendous emotional distress and damage to her mental health."
It is further stated that several of Markle's friends "had never seen her in this state before" and that they "were rightly concerned for her welfare, specifically as she was pregnant, unprotected by the Institution, and prohibited from defending herself.”
Additionally, it is claimed in the documents that "it was mandated by the [Kensington Palace Communications Team] that all friends and family of [Markle] should say 'no comment' when approached by any media outlet, despite misinformation being provided to UK tabloids about [her]."
"This shared frustration amongst [her] friends left everyone feeling silenced, as it appeared that other so-called sources were able to disseminate false statements," the documents continue. "While the people who knew her best were told that they needed to remain silent."
A large portion of the new documents also refer to an article published by People that included anonymous interviews with several of Markle's friends in which they defended her against claims made in Mail on Sunday's controversial report.
Markle claims that she was unaware that any of her friends had spoken to People regarding her father or the letter she had written to him. It's claimed that she was informed about the article by Prince Harry the day it was published and that she did not know which of her friends were involved until "a considerable time later."
It is further stated that Markle believes the palace's position of silence may have been the impetus for her friends to seek out People.
"It is probably because of this reason, as well as concerns about the press intrusion by the UK tabloids, that a few friends chose to participate, and they did so anonymously," the docs state.
Another behind-the-scenes aspect of the Markle family drama revealed in the new docs revolved around the accommodations Markle claims she made for her father to come to her wedding -- which he ultimately did not attend.
This included booking flights on his behalf, booking and securing accommodations and lodgings and arranging for the creation of multiple custom-made suits and outfits for her father to wear throughout the "wedding week."
The trail over the lawsuit between the Sussexes and the publication is expected to begin later this year. For more on the ongoing legal drama, see the video below.