Meghan, the Duchess of Sussex, has sued the publisher of a British tabloid newspaper, claiming that it illegally published a private letter she sent to her estranged father. Prince Harry said he and his wife — an American actress known as Meghan Markle before the couple married in 2018 — decided after "many months" to take legal action against the Mail on Sunday newspaper over what he called a "ruthless campaign" to smear Meghan.

The royal couple accused the tabloid and its parent company, Associated Newspapers, of misusing private information, infringement of copyright and breach of a U.K. data protection act brought into force in 2018, according to an official statement. The publisher also owns the Daily Mail newspaper and MailOnline.

"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," the statement read. The statement called the publication of the personal letter just one example in a "long and disturbing pattern of behaviour."

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Schillings, the law firm handling the case, said the Mail on Sunday was part of "a campaign by this media group to publish false and deliberately derogatory stories about [Meghan], as well as her husband."

The Duke and Duchess of Sussex have also accused the Mail on Sunday of editing the letter. Prince Harry wrote: "In addition to their unlawful publication of this private document, they purposely misled you by strategically omitting select paragraphs, specific sentences, and even singular words to mask the lies they had perpetuated for over a year."

Associated Newspapers said in a statement provided to CBS News that it "stands by the story it published and will be defending this case vigorously."

"Specifically, we categorically deny that the Duchess' letter was edited in any way that changed its meaning," a spokesperson for the publisher said.

Prince Harry cited the "painful" impact of intrusive press coverage as the catalyst for them taking legal action. He also referred to his late mother, Princess Diana, who died in a car crash in 1997 as the car she was in was followed through the streets of Paris by paparazzi.

"[M]y deepest fear is history repeating itself," he wrote. "I've seen what happens when someone I love is commoditised to the point that they are no longer treated or seen as a real person. I lost my mother and now I watch my wife falling victim to the same powerful forces," said Harry, who was 12 years old when his mother died.

The lawsuit is being privately funded by the Duke and Duchess of Sussex. The statement said any monetary damages resulting from the case would be donated to an anti-bullying charity.

Meghan and Prince Harry have been on tour this week in southern Africa, along with their newborn son, Archie. They were together in Cape Town on Wednesday, the last day of their tour.

The royal couple's tense relationship with the press was visible Tuesday as Harry chastised a reporter for asking a seemingly harmless question as he left an official engagement. He frowned and told the journalist not to "make it like this," as he ignored the question and climbed into his Range Rover.

Prince Harry's biographer, Penny Junor, said Wednesday that she understands why Harry wanted to protect his wife — but added "this seems like an over-emotional and somewhat ill-advised outburst."