Overnight on Friday, New Zealand time, High Court Justice Sir Mark Warby ruled against the duchess, striking out parts of her case. Her team will not be able to make the case that the Mail "stirred up" issues with her father Thomas Markle, that they had an "agenda" against her, and that they acted dishonestly.
Despite this setback, this is only round one in what could be a lengthy legal showdown.
While other members of the royal family (including Diana Princess of Wales, Prince Charles and the Queen) have sued newspapers before, they were usually matters that were concluded relatively swiftly.
This case, instead, looks set to be a much lengthier affair with the Duchess' relationship with her estranged father Thomas at the very centre of proceedings.
Here's what you need to know:
THE LEGAL EAGLES
Pinstripe politesse? Puh-lease. The Sussexes have brought some super star power to proceedings in their choice of a legal team. (Or, as the Times put it: "Instead of buttoned-up legal representatives, the Sussexes have instructed a cadre of rottweilers.")
Spearheading their case is barrister David Sherborne whose former clients include Michael Douglas, Catherine Zeta-Jones, Sir Paul McCartney, Hugh Grant and Diana, Princess of Wales early on in his career.
Also on Meghan's side is the high-profile law firm of Schillings, where partner Jenny Afia is taking charge of the royals' case.
Afia, in 2019, told a magazine that she wanted to have "two of the world's most influential women … as my clients".
Representing Associated Newspaper is Antony White QC, a barrister who previously co-founded a predominantly human-rights related practice with Cherie Blair and others.
He has also represented Naomi Campbell in successfully suing the Daily Mirror.
THE LETTER THAT STARTED EVERYTHING
In August 2018 Meghan sent a five-page handwritten letter to her father, Thomas Markle in Mexico.
She did this after it was revealed her father had been staging photos with the paparazzi and had missed her May 2018 wedding.
After the story about the staged pictures hit the headlines, Thomas, who had been slated to walk his daughter down the aisle, was hospitalised with heart problems and declined to attend the nuptials.
The following February, People magazine published a cover story entitled "Meghan Markle's friends break their silence: We Want to Speak the Truth" which quoted five anonymous friends of the Duchess.
They claimed that Thomas, an Emmy-winning TV lighting director, had not called or texted his daughter despite her letter.
In the article, they said: "He knows how to get in touch with her … He's never called; he's never texted. It's super painful."
Days later, the Mail published excerpts of the letter in question under the headline "Revealed: The letter showing true tragedy of Meghan's rift with a father she says has 'broken her heart into a million pieces'."
High Court Justice Sir Mark Warby, who is overseeing the case, will have to decide whether the Duchess had a "reasonable expectation" that her letter would remain private.
THE BOMBSHELL ANNOUNCEMENT
In October last year, Meghan announced that she was suing Associated Newspapers for publishing excerpts of her letter in five articles.
More specifically, she is suing over misuse of private information, copyright infringement, and breach of the Data Protection Act 2018.
At the same time the couple revealed their legal fightback, Harry penned a deeply emotional statement condemning what he termed the "ruthless campaign" against Meghan, writing: "I lost my mother and now I watch my wife falling victim to the same powerful forces."
Subsequently, Thomas told the Daily Mail: "I decided to release parts of the letter because of the article from Meghan's friends in People magazine. I have to defend myself. I only released parts of the letter because other parts were so painful. The letter didn't seem loving to me. I found it hurtful."
Associated Newspapers has said it will "vigorously" defend the case.
THE MYSTERY MATES
This is where the People story comes back into things.
Associated Newspapers has argued that the letter was already in the public domain after Meghan's mates made reference to it in the earlier US magazine story.
Meghan has denied having any knowledge that her unnamed pals were speaking to People.
Papers filed by her legal team state " … the truth is that the author did not know that such an interview had been given or, more importantly, that any reference would be made to the letter…".
However, per the (UK) Telegraph, "the defence claims she cannot have been unaware they were giving such a high profile, off the record interview about her".
It said: "The People interview depicted Mr Markle as having acted unreasonably and unlovingly, having cold-shouldered his daughter, and being solely to blame for the estrangement between father and daughter. This was a one-sided and/or misleading and false narrative."
THE EMOTIONAL TEXTS
Meghan's team has submitted in evidence a number of texts in which the Sussexes attempted to speak to Thomas in the run up to their wedding.
In one Harry wrote, "Any speaking to the press WILL backfire, trust me Tom. Only we can help u, as we have been trying from day 1".
In another, Meghan said "I've called and texted but haven't heard back from you so hoping you're okay".
THE HANDWRITING ARGUMENT
Prior to becoming a successful actress, Meghan worked doing freelance calligraphy, including doing the wedding invitations for Robin Thicke and Paula Patton's 2005 nuptials. Her particularly elegant script has also been drawn into this case.
Associated Newspapers has claimed that her "elaborate" handwriting is proof that the former Suits star expected the letter to be read by other people.
Meghan has denied this and says the letter was "originally drafted in electronic form and then written out in longhand".
She also denied knowing or believing Thomas would disclose the letter to the press.
SO, MEGHAN LOST ROUND ONE
Yep.
Last week during the preliminary hearing, her team had argued that they should be allowed to make the case that the paper had an "obvious agenda of publishing intrusive or offensive stories" about the royal and had "stirred up" issues with Thomas.
However, in the written ruling released on Friday night, Mr Justice Warby has struck out those claims, writing: "Some of the allegations are struck out as irrelevant to the purpose for which they are pleaded.
"Some are struck out on the further or alternative ground that they are inadequately detailed.
"I do not consider that the allegations struck out on that basis go to the 'heart'; of the case, which at its core concerns the publication of five articles disclosing the words of, and information drawn from, the letter written by the claimant to her father in August 2018."
However, he did leave the door open to potentially re-introducing some of the claims, saying "Some aspects of the case that I have struck out at this stage may be revived if they are put in proper form".
What impact this ruling will have on her case depends on who you listen to.
The Times reports that her law firm Schillings has said: "Today's ruling makes very clear that the core elements of this case do not change and will continue to move forward. The duchess's rights were violated; the legal boundaries around privacy were crossed."
However, Howard Kennedy partner Mark Stephens has told the Mail Online: "For Meghan this judgment is like a train ploughing into a petrol tanker on a level crossing. It is a complete disaster. She has been humiliated today."
WHAT HAPPENS NEXT
Not much for the time being. A date has not been set for the full trial which could happen later this year or in 2021.
WILL MEGHAN TAKE THE STAND
Potentially.
Sherborne told proceedings: "The defendant (Associated Newspapers) wants to cross-examine her (Meghan) as to whether that belief is reasonable or not – and they can do that."
HOW ABOUT THOMAS?
Again, maybe. In January this year, it was reported that Thomas Markle had agreed to be a witness for the Mail on Sunday.
THE COURTROOM SHOWDOWN
Meghan and Thomas have not seen one another in person for at least two years. When the hearing starts in full, it is possible that father and daughter's first physical reunion will take place from either side of a London courtroom.
HOW MUCH IS THIS COSTING?
Estimates for how much this is costing the Sussexes alone have varied, from more than $110,000 to up to $670,000. No matter which side comes out on top legally at the end of all of this, the lawyers involved on both sides look set to be the ultimate winners.
THE WAITING GAME
While a date has not been set as yet for the full hearing but one thing is for sure: The world's eyes will be glued to proceedings.
