The publication of a letter from the Duchess of Sussex to her father was a "triple-barrelled invasion" of her privacy, the High Court has been told.
Thomas Markle says he allowed the Mail to publish portions of the letter to "set the record straight" after reading the People article.
Her lawyers have applied for summary judgment, a legal step which would see parts of the case resolved without a trial and without the need for witnesses, but the newspaper argues the case is 'wholly unsuitable for summary judgment'.
Her lawyer Justin Rushbrooke even told Huffington that Associated Newspapers had "no real prospect" of winning the case.
They claim the publication of extracts from the private, handwritten letter to Thomas Markle was "self-evidently. highly intrusive".
The Duchess of Sussex launched legal action against Associated Newspapers, which publishes the Mail on Sunday and MailOnline website, for printing extracts of the letter to Thomas Markle. The couple are now living in the U.S. with their son Archie.
He said the decision to publish the letter was an assault on "her private life, her family life and her correspondence".
"We say that, actually, at its heart, it is a very straightforward case about the unlawful publication of a private letter", he said.
The paper published extracts in February the following year, and has justified its action by saying it allowed Markle to respond to interviews Meghan's anonymous friends had given to the US magazine People.
Rushbrooke said Meghan's five-page letter, sent in August 2018, was "a message of peace" intended for her father alone.
Meghan wanted to use the letter "as part of a media strategy" and discussed it with royal communications officials before it was sent, it argued.
The letter was sent to the parties on behalf of Jason Knauf - formerly communications secretary to the Duke and Duchess of Sussex, whom the newspaper claims was involved in the wording of Meghan's letter - and Christian Jones, their former deputy communications secretary.
He said the "contents and character of the letter were intrinsically private, personal and sensitive in nature" and that Meghan "had a reasonable expectation of privacy in respect of the contents of the letter".
In a written witness statement submitted by the defence, he said the article "had given an inaccurate picture of the contents of the letter and my reply and had vilified me by making out that I was dishonest, exploitative, publicity-seeking, uncaring and cold-hearted, leaving a loyal and dutiful daughter devastated".
"Lots of members of the royal family are freeloading off the idea of the royal family", he said.
In Thomas Markle's evidence, he said the letter "signalled the end" of his relationship with his daughter, and instead of a reconciliation attempt, the letter was a "criticism" of him.
He told the court, "It is a letter that was. not written in anger but written in sorrow, by a daughter who clearly felt she had reached a breaking point in her relationship with her father".
He also said that he "had never meant to talk publicly about Meg's letter to me", but he felt the People article "vilified me by making out that I was dishonest, exploitative, publicity-seeking, uncaring and cold-hearted, leaving a loyal and dutiful daughter devastated".
He said he had "never meant to talk publicly about Meg's letter" until he read the People magazine piece which, he claimed, suggested he was "to blame for the end of the relationship".
A full trial was due to take place at the High Court in January, but a year ago the case was adjourned until autumn 2021 for a "confidential" reason.
This interim remote hearing - to consider the request for summary judgement - is due to last two days.
However, in a ruling in November, Mr Justice Warby said Mr Markle's "thoughts and feelings" about the letter were "a relatively minor aspect of the case overall".