Johannesburg, South Africa CNN  — 

Meghan, the Duchess of Sussex, is suing a British newspaper, alleging that it illegally published a private letter to her father, as her husband Prince Harry launched an extraordinary and emotional attack on UK tabloids.

Harry accused the Mail on Sunday of selectively editing the letter to disguise “lies” the paper had told about the Duchess – a claim that the tabloid specifically denies.

And he alleged the British tabloid press was waging a campaign against Meghan that mirrored the treatment meted out to his mother, Princess Diana, who died in 1997 when her car crashed as it was being chased by a paparazzo on a motorbike.

“Unfortunately, my wife has become one of the latest victims of a British tabloid press that wages campaigns against individuals with no thought to the consequences – a ruthless campaign that has escalated over the past year, throughout her pregnancy and while raising our newborn son,” Harry wrote in an online statement

Harry wrote the statement himself, and it was published unedited, a royal source said. The Queen and Harry’s father, the Prince of Wales, were informed of the proceedings, the source told CNN.

The royal source added that the lawsuit relates to a story published by the Mail on Sunday in February, which was based on a handwritten letter purportedly sent by Meghan to her estranged father, Thomas Markle, shortly after the Duke and Duchess got married last year.

When the Mail on Sunday printed the Duchesses’ personal letter, it was redacted substantially, said the royal source.

“This particular legal action hinges on one incident in a long and disturbing pattern of behavior by British tabloid media,” Harry wrote in his statement. “The contents of a private letter were published unlawfully in an intentionally destructive manner to manipulate you, the reader, and further the divisive agenda of the media group in question.”

Meghan, Duchess of Sussex, visits Action Aid to participate in discussions during the royal tour of South Africa on October 01, 2019 in Johannesburg.

Law firm Schillings, which is representing the Duchess, said legal proceedings had been initiated against the Mail on Sunday, and its parent company Associated Newspapers, over the misuse of private information, infringement of copyright and breach of the UK’s Data Protection Act 2018.

A Mail on Sunday spokesman said: “The Mail on Sunday stands by the story it published and will be defending this case vigorously. Specifically, we categorically deny that the Duchess’s letter was edited in any way that changed its meaning.”

Asked about the announcement of the lawsuit, John Wellington, managing editor of The Mail on Sunday, would not comment on when paper found out about the lawsuit, or on which law firm was representing the company.

Harry and Meghan are currently traveling in southern Africa. The timing of the lawsuit is not related to their travels, but rather to specific legal advice, a palace source told CNN Tuesday. The source asked not to be named discussing the couple’s private business.

But royal commentator Richard Fitzwilliams described the lawsuit’s timing as “unprecedented.”

“The timing of this, before one of the most successful tours in royal history has ended, is truly unprecedented,” Fitzwilliams said in a statement. “Since [the Duchess] owns the copyright of her correspondence she is likely to have been advised that they have an excellent chance of winning the case though it will bring issues regarding her family to the fore.”

“One must assume that they expect this case to be settled out of court which is customary for cases involving the royals.” Fitzwilliams added that only four royals had appeared in court before: the Prince of Wales (later King Edward VII) in 1870 and 1891, Viscount Linley (the son of Princess Margaret) in 1990 and the Princess Royal in 2002. “If this were to go to court it would be sensational,” he concluded.

David Banks, a journalist and expert in media law, told the PA news agency that if the action did end up in court “it could be the privacy case of the century.”

Banks added that a trial could ultimately backfire against the Sussexes and lead to more disclosures about the Duchess’ relationship with her father. He also cited the case of singer Cliff Richards, who successfully sued the BBC over its coverage of a 2014 police raid on his home which resulted from a sexual assault allegation. The singer denied the allegation and never faced charges.

During the lawsuit against the BBC, Richards appeared in court and detailed the effect the reporting had on him, Banks said.

“It would be very powerful if Meghan does or Harry does as well. It is very unusual for royals to do. I can’t think of a case in living memory,” he added.