Prince Harry has blamed the U.K. tabloids for the breakdown of his relationship with ex-girlfriend Chelsy Davy.

On Tuesday, the Duke of Sussex stepped into a courtroom witness box to hold the British press accountable for its "destructive" role throughout his life. The 38-year-old is the first senior member of the British royal family to testify in over a century as he held a Bible in his right hand and, in a soft voice, swore to tell the "whole truth and nothing but the truth" in the High Court in London.

The youngest son of King Charles III accuses the publisher of the Daily Mirror of using unlawful techniques on an "industrial scale" to score front-page scoops on his life.

In a written testimony filed to the High Court in London, Harry said "the prying eyes of the tabloids" strained his relationship with the Zimbabwe-born businesswoman. He noted it was "the main factor" in why they decided to call it quits.

Prince Harry in military uniform next to Chelsy Davy in a close-up photo

Prince Harry said tabloids were "the main factor" for his breakup with ex-girlfriend Chelsy Davy. ( Anwar Hussein/WireImage)

"Prince Harry is driving, looking in the rearview mirror," British royal expert Hilary Fordwich told Fox News Digital. "His relationship with Chelsy was long before Meghan Markle. How on earth must Meghan be feeling that he is dwelling on a lost love to this day?"

According to Harry, the couple met in early 2004 and were in an on-and-off relationship until mid-2010.

"Our relationship was long distance for the majority of the time we were together, with Chelsy and I often living in different countries, so we relied on communicating by phone a lot," Harry wrote. "We, naturally, spoke about all types of personal matters, including all aspects of our relationship and this was often through voicemail. As my girlfriend, I trusted Chelsy with the most private of information and vice versa."

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Prince Harry gets out of car at court

Prince Harry arrives to give evidence at the Mirror Group Phone hacking trial at the Rolls Building at High Court on June 6, 2023, in London. (Leon Neal/Getty Images)

Much of Harry’s case against Mirror Group Newspapers, focuses on details he believed were leaked concerning his relationship with Davy, 37, The New York Times reported. He claimed newspaper articles routinely mentioned private conversations that wouldn’t have been obtained without using illicit means.

Court sketch of Prince Harry in court speaking to a barrister

Court artist sketch by Elizabeth Cook of the Duke of Sussex (left) with his counsel David Sherborne (right) giving evidence at the Rolls Buildings in central London, with Mr. Justice Fancourt (centre) looking on, during the phone hacking trial against Mirror Group Newspapers (MGN). (Elizabeth Cook/PA via Alamy)

Harry pointed out one article that alleged Davy gave him "a tongue-lashing down the phone" for flirting with another woman at a party. In his written testimony, Harry said the details of their phone conversations weren’t attributed to sources. He also mentioned another article that described "an emotional phone call" involving Davy.

Harry said he was at a "complete loss" as to how such private details about his vacations with Davy would be obtained. He said both journalists and photographers would arrive at their hotel off the coast of Mozambique before they did.

Prince Harry in a sports uniform laughing with Chelsy Davy wearing a scarf

"We met in about early 2004 and were in a relationship which continued, on and off, until around mid-2010," Prince Harry wrote in his testimony. (Getty Images)

"I don’t believe that my girlfriend would ever have spoken to a passenger on a plane about our relationship," Harry noted.

"We could also never understand how private elements of our life together were finding their way into the tabloids, and so our circle of friends became smaller and smaller," said Harry. "I remember finding it very hard to trust anyone, which led to bouts of depression and paranoia."

Harry admitted he regretted cutting friends out of his life out of fear they were the sources of the leaks.

The case dates from 1996 to 2011.

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Chelsy Davy wearing a blue dress and matching fascinator

Chelsy Davy is seen here at the wedding of Prince Harry and Meghan Markle in 2018. (Pool/Max Mumby/Getty Images)

"I genuinely feel 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," said Harry.

Davy, now Chelsy Yvonne Cutmore-Scott, married her boyfriend of three years, Sam Cutmore-Scott, in early 2022. They share a son named Leo. Davy, as well as Harry’s other ex-girlfriend Cressida Bonas, were guests at Harry’s wedding in 2018.

Meghan Markle, a former American actress, became the Duchess of Sussex when she married the British prince.

"You have to wonder what Meghan makes of Harry's testimony regarding Chelsy," Christopher Andersen, author of "The King," said to Fox News Digital. "They were together for eight years and seemed headed for the altar. Is the assumption here that Chelsy was really Harry's first choice and that they would have married if it hadn't been for the intrusive tabloid press?  Meghan can't be too happy about that, I would imagine."

Prince Harry in a blue suit waves for photos as he walks out with his new fiancée Meghan Markle, wearing white and putting her hand up in the air

Meghan Markle, an American actress, became the Duchess of Sussex when she married Prince Harry in 2018. (Daniel Leal/AFP)

"Chelsy did say after their final breakup that all the tabloid press attention was crazy, full-on, just too much for her to bear," Andersen continued. "She was a free spirit and wanted something approaching a normal life – and she knew she'd never have that being Harry's wife. The specter of living her life in a royal fishbowl proved too much, and she fled back home to Zimbabwe."

"Chelsy Davy is incredibly private, rejected the limelight, and has a brand-new baby," Kinsey Schofield, host of the "To Di For Daily" podcast, told Fox News Digital. "I highly doubt she enjoys Harry rehashing her youth as she navigates motherhood. And as a likely victim of such an egregious violation of her personal life... I do hope that she was warned or asked permission before Harry decided to reopen this wound."

In 2016, Davy admitted to The Times that she was "just a normal kid" while she was dating Harry, and it was "tough" to face the media scrutiny.

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A close-up of Chelsy Davy wearing a patterned dress

Chelsy Davy has previously spoken out about the struggles she endured being in the spotlight. (Niki Nikolova/FilmMagic)

"It was horrible," she said. "It was nuts. That’s also why I wanted to go back to Africa. Now it’s calm, it’s fine."

Mirror Group Newspapers attorney Andrew Green asked Harry to identify what evidence he had of phone hacking in specific articles, and Harry repeatedly said he’d have to ask that question of the journalist who wrote it. He continually insisted that the manner in which information had been obtained was highly or incredibly suspicious.

He said some of the journalists had been known for hacking or that there were invoices to third parties, including private investigators known for snooping, around the time of the articles.

Harry has made a mission of holding the U.K. media to account for what he sees as their hounding of him and his family.

Prince Harrys book Spare on display at a store

Prince Harry has expressed his fury toward the British press in his memoir "Spare," which was published in January. (Lev Radin/Pacific Press/LightRocket)

Setting out the prince’s case in court Monday, his lawyer, David Sherborne, said that from Harry’s childhood, British newspapers used hacking and subterfuge to mine snippets of information that could be turned into front-page scoops.

He said stories about Harry were big sellers for the newspapers, and around 2,500 articles had covered all facets of his life during the time period of the case – 1996 to 2011 – from injuries at school to experimenting with marijuana and cocaine, to ups and downs with girlfriends.

"Nothing was sacrosanct or out of bounds" for the tabloids, the lawyer said.

Mirror Group has paid more than 100 million pounds ($125 million) to settle hundreds of unlawful information-gathering claims and printed an apology to phone hacking victims in 2015.

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Prince Harry and Meghan Markle smile while riding in a carriage.

The Duke and Duchess of Sussex reside in California with their two young children, Prince Archie and Princess Lilibet. They stepped down as senior royals in 2020. (Samir Hussein/Samir Hussein/WireImage)

But the newspaper denies or hasn’t admitted any of Harry’s claims.

Green said Monday there was "simply no evidence capable of supporting the finding that the Duke of Sussex was hacked, let alone on a habitual basis."

The Duke of Sussex currently resides in California with his wife and their two young children.

The Associated Press contributed to this report.