Prince Harry has taken the stand.

The Duke of Sussex arrived at London's High Court on June 6 to testify in the phone hacking case against Mirror Group Newspapers, becoming the first senior British royal to testify in a court of law in more than a century.

In his 55-page witness statement, published in full by the New York Times, Harry wrote that he "genuinely feels that in every relationship that I've ever had—be that with friends, girlfriends, with family or with the army, there's always been a third party involved, namely the tabloid press."

Harry's case, according to the BBC (which was filed in 2019), involves 148 articles published between 1996 and 2010. His testimony comes nearly a month after MGN, which owns publications including Daily Mirror, Sunday Mirror, and Daily Express, apologized to the Duke of Sussex for a single instance of unlawfully gathering information amid the start of the trial.

"MGN unreservedly apologises for all such instances of UIG," the publisher's statement—written in a May 10 court filing—read, per the BBC, "and assures the claimants that such conduct will never be repeated." The company added that the violation in question, which isn't part of his lawsuit against MGN, "warrants compensation."

The apology also came one month after it was revealed that Harry's brother Prince William had privately settled in the phone-hacking case for a "very large sum."

During his testimony, the Duke of Sussex touched on everything from his late mother Princess Diana's relationship with the press to his split from ex Chelsy Davy.

Buckingham Palace is not commenting on the ongoing trial.

Keep reading for every bombshell from his High Court appearance.

Prince Harry Blames the Press for Breakup With Chelsy Davy

In his written statement published by the NYT, the Duke of Sussex alleged that press intrusion put "a huge amount of unnecessary stress and strain" on his relationship with Chelsy Davy, whom he dated on-and-off from 2004 until 2010. He also recalled a trip with Chelsy to Bazaruto, in which he claims journalists and photographers from MGN, as well as other agencies, were able to arrive and "book into the hotel before we got there."

"I now believe they had blagged our flight details and hotel bookings and/or intercepted our voicemails," he wrote. "We were never on our own and able to enjoy each other's company away from the prying eyes of the tabloids."

Prince Harry added that the pressure "led her to make the decision that a royal life was not for her, which was incredibly upsetting for me at the time."

Princess Diana Believed Her Private Messages Were Listened To

Prince Harry claimed in his written statement that his late mother Princess Diana also believed her private messages were listened to using unlawful methods in the months leading up to her August 1997 death—a notion that makes him "feel physically sick."

More specifically, he pointed out that he was "shocked, disgusted and appalled when I was shown by my solicitors three hand-written letters from her to the well-known television personality Michael Barrymore," a British comedian and friend of the late royal. Harry went on to note an alleged passage from a March 1997 letter addressed to him, claiming that the press was aware of private details of their friendship.

"I was devastated tonight to hear that the Daily Mirror have [sic] been telephoning my office to ask details about six meetings that are supposed to have taken place between us nobody around me knew of our Sunday evening plan," she writes, according to his statement, "I would never do anything to cause you any personal distress & it only remains for me to say how deeply sorry I am that what I considered to be a private and precious matter has become public property."

Harry writes that he "can only assume that this information had been obtained via voicemail interception and/or other unlawful information gathering such as live land linetapping."

According to The Guardian, The Mirror responded about the claim that Diana's voicemails were hacked, stating that it is "total speculation without any evidential basis whatsoever."

Prince Harry Calls Out Piers Morgan for Princess Diana Coverage

In his statement, the Duke of Sussex also addressed commentator Piers Morgan directly, who served as the editor of the Daily Mirror from 1995 until 2004.

"The thought of Piers Morgan and his band of journalists earwigging into my mother's private and sensitive messages (in the same way as they have me)," he writes, "and then having given her a nightmare time three months prior to her death in Paris, makes me feel physically sick and even more determined to hold those responsible, including Mr. Morgan, accountable for their vile and entirely unjustified behaviour."

E! News has reached to Morgan for comment and has not heard back.

Prince Harry Addresses Reports of James Hewitt Being His Biological Father

The royal also addressed reports of rumors that former cavalry officer James Hewitt—who claimed to have an affair with Princess Diana during her marriage to the-now King Charles—was his biological father.

"Numerous newspapers had reported a rumour that my biological father was James Hewitt, a man my mother had a relationship with after was born," Harry writes in his statement. "At the time of this article and others similar to it, I wasn't actually aware that my mother hadn't met Major Hewitt until after was born."

He also explained how the timing of the reports managed to hurt him even further.

"At the time, when I was 18 years old and had lost my mother just six years earlier, stories such as this felt very damaging and very real to me," he continued. "They were hurtful, mean and cruel. I was always left questioning the motives behind the stories. Were the newspapers keen to put doubt into the minds of the public so might be ousted from the Royal family?"

This isn't the first lawsuit the Duke of Sussex has filed against a tabloid belonging to the publisher, as the royal is also in the midst of an ongoing defamation case against the Mail on Sunday.

In July, Prince Harry won the first stage of his case against the publication. A High Court judge ruled that parts of an article published by the U.K. based newspaper, which discussed Harry's legal case against the government over security arrangements, were, in fact, defamatory. 

E! News reached out to the Mail on Sunday at the time of the ruling and the publication declined to comment.