The Duke and Duchess of Sussex have announced they are taking legal action against the Mail on Sunday after the newspaper allegedly unlawfully published one of the duchess’ private letters.

In a lengthy and highly personal statement published on the royal couple’s official website, Prince Harry said they had been driven to take legal action after the “painful” impact of “relentless propaganda” against his wife from the British tabloid press.

Referencing press coverage of his mother Princess Diana, the duke said his “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.”

Prince Harry and Meghan Markle – in pictures Show all 55 1 /55 Prince Harry and Meghan Markle – in pictures Prince Harry and Meghan Markle – in pictures September 2017 Prince Harry and Meghan Markle at the Invictus Games in Toronto, Canada. The Invictus Games is an international sport event for wounded, injured and sick (WIS) servicemen and women, both serving and veteran. It was created by the Duke of Sussex and aims to use the power of sport to inspire recovery, support rehabilitation and generate a wider understanding of all those who serve their country Invictus Games Foundation/Getty Prince Harry and Meghan Markle – in pictures November 2017 Prince Harry and Meghan Markle pose for a photograph in the Sunken Garden at Kensington Palace following the announcement of their engagement AFP/Getty Prince Harry and Meghan Markle – in pictures November 2017 Meghan Markle shows off her engagement ring AFP via Getty Prince Harry and Meghan Markle – in pictures December 2017 Prince William, Duke of Cambridge, Prince Philip, Duke of Edinburgh, Catherine, Duchess of Cambridge, Meghan Markle and Prince Harry attend Christmas Day Church service at Church of St Mary Magdalene in King's Lynn Getty Prince Harry and Meghan Markle – in pictures January 2018 Prince Harry and Meghan during a visit to Reprezent 107.3FM in Pop Brixton. The Reprezent training programme was established in Peckham in 2008, in response to the alarming rise in knife crime, to help young people develop and socialise through radio Getty Prince Harry and Meghan Markle – in pictures January 2018 Meghan Markle greets well-wishers on arrival at Cardiff Castle for a day showcasing the rich culture and heritage of Wales AFP via Getty Prince Harry and Meghan Markle – in pictures January 2018 The couple watching a dance performance by Jukebox Collective during their to Cardiff Castle AFP via Getty Prince Harry and Meghan Markle – in pictures February 2018 Prince Harry and Meghan Markle walk through the corridors of the Palace of Holyroodhouse on their way to a reception for young people in Edinburgh. The reception celebrated youth achievements, marking Scotlands Year of Young People 2018, an initiative that aims to inspire Scotland through its young people: celebrating their achievements, strengthening their voice on social issues and creating new opportunities for them to shine AFP Prince Harry and Meghan Markle – in pictures February 2018 Prince Harry, Meghan Markle, Catherine, Duchess of Cambridge and Prince William at the first annual Royal Foundation Forum in London. Under the theme 'Making a Difference Together', the event showcased the programmes run or initiated by The Royal Foundation Getty Prince Harry and Meghan Markle – in pictures March 2018 Prince William, Kate, Meghan and Prince Harry attend a Commonwealth Day Service at Westminster Abbey AFP via Getty Prince Harry and Meghan Markle – in pictures March 2018 Meghan Markle greets well-wishers after a visit to one of Belfast's most historic buildings, The Crown Liquor Saloon, a former Victorian gin palace, now run by the National Trust. It was the Royal couple's first joint visit to Northern Ireland AFP via Getty Prince Harry and Meghan Markle – in pictures April 2018 Prince Harry and Meghan Markle meet participants as they attend the UK team trials for the Invictus Games Sydney 2018 at the University of Bath AFP via Getty Images Prince Harry and Meghan Markle – in pictures May 2018 Meghan Markle and her mother, Doria Ragland arriving at Cliveden House Hotel the night before her wedding to Prince Harry Getty Prince Harry and Meghan Markle – in pictures May 2018 Royal fans sing for the television in Windsor the day before the Royal wedding AFP via Getty Prince Harry and Meghan Markle – in pictures May 2018 Meghan Markle walks down the aisle in St George's Chapel, Windsor Castle, during her wedding AFP via Getty Prince Harry and Meghan Markle – in pictures May 2018 Prince Harry and Meghan Markle stand facing each other hand-in-hand before Archbishop of Canterbury Justin Welby during their wedding ceremony AFP via Getty Prince Harry and Meghan Markle – in pictures May 2018 Prince Harry kisses the Duchess of Sussex, as they pass through the Cambridge Gate into the grounds of Windsor Castle at the end of their carriage procession AFP via Getty Prince Harry and Meghan Markle – in pictures May 2018 The newly married royals leave Windsor Castle after their wedding to attend an evening reception at Frogmore House AFP via Getty Prince Harry and Meghan Markle – in pictures June 2018 Queen Elizabeth II sitts and laughs with Meghan, Duchess of Sussex during a ceremony to open the new Mersey Gateway Bridge in the town of Widnes in Halton, Cheshire Getty Prince Harry and Meghan Markle – in pictures June 2018 Prince Harry and Meghan return in a horse-drawn carriage after attending the Queen's Birthday Parade, 'Trooping the Colour' on Horseguards parade AFP via Getty Prince Harry and Meghan Markle – in pictures July 2018 Prince Charles, Prince of Wales, Camilla, Duchess of Cornwall, Queen Elizabeth II, Meghan, Duchess of Sussex, Prince Harry, Duke of Sussex, Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge watch the RAF flypast on the balcony of Buckingham Palace, as members of the Royal Family attend events to mark the centenary of the RAF Chris Jackson/Getty Prince Harry and Meghan Markle – in pictures July 2018 Meghan and Prince Harry kiss after the Sentebale Polo event that was held at the Royal County of Berkshire Polo Club Getty Prince Harry and Meghan Markle – in pictures August 2018 The Duke and Duchess of Sussex meet the cast and crew of "Hamilton" backstage after the gala performance in support of Sentebale at Victoria Palace Theatre Getty Prince Harry and Meghan Markle – in pictures September 2018 Meghan meets 7-year-old Matilda Booth during the annual WellChild awards at Royal Lancaster Hotel in London Getty Prince Harry and Meghan Markle – in pictures October 2018 Prince Harry and Meghan meet 98-year-old Daphne Dunne during a meet and greet at the Sydney Opera House during an official 16-day Autumn tour visiting cities in Australia, Fiji, Tonga and New Zealand Getty Prince Harry and Meghan Markle – in pictures October 2018 Prince Harry and Meghan meet a koala named Ruby and its koala joey named Meghan after the Duchess of Sussex during a visit to Taronga Zoo in Sydney AFP via Getty Prince Harry and Meghan Markle – in pictures October 2018 Prince Harry looks on as his wife Meghan, the Duchess of Sussex, is hugged by student Luke Vincent of Buninyong Public School following the couple's arrival at Dubbo Regional Airport in Dubbo AFP via Getty Prince Harry and Meghan Markle – in pictures October 2018 Harry and his wife Meghan watch aboriginal dances at Victoria Park in Dubbo AFP via Getty Prince Harry and Meghan Markle – in pictures October 2018 The Duke and Duchess of Sussex meet with lifeguards at South Melbourne Beach. BeachPatrol is a network of volunteers who are passionate about keeping Melbourne's beaches and foreshores clear of litter to reduce the negative impact of litter on the marine environment and food chain, and provide a safe environment for the public to enjoy their local beach Getty Prince Harry and Meghan Markle – in pictures October 2018 Prince Harry and Meghan join a circle during a "Fluro Friday" session run by OneWave, a local surfing community group who raise awareness for mental health and wellbeing, at Sydney's iconic Bondi Beach AFP Prince Harry and Meghan Markle – in pictures October 2018 The British royals kicked off their shoes and donned tropical garlands on Bondi Beach AFP via Getty Prince Harry and Meghan Markle – in pictures October 2018 Prince Harry and Meghan visit an exhibition of Tongan handicrafts, mats and tapa cloths at the Fa'onelua Convention Centre in Nuku'alofa, Tonga Getty Prince Harry and Meghan Markle – in pictures October 2018 Prince Harry and Meghan laying a wreath at the National War Memorial in Wellington, New Zealand Getty Prince Harry and Meghan Markle – in pictures October 2018 Prince Harry and his wife Meghan visit Redwoods Tree Walk in Rotorua AFP via Getty Prince Harry and Meghan Markle – in pictures November 2018 Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge, Prince Harry, Duke of Sussex and Meghan, Duchess of Sussex at a service marking the centenary of WW1 armistice at Westminster Abbey Getty Prince Harry and Meghan Markle – in pictures February 2019 The Duke and Duchess of Sussex, visit the Kasbah of the Udayas near the Moroccan capital Rabat AFP via Getty Prince Harry and Meghan Markle – in pictures March 2019 Prince Harry and Meghan speak on stage during WE Day UK 2019 at The SSE Arena in London Getty Prince Harry and Meghan Markle – in pictures March 2019 Meghan and Prince Harry react as they are presented with baby gifts by Canadian High Commissioner to the United Kingdom, Janice Charette, at Canada House, during an event to mark Commonwealth Day, in central London AFP via Getty Prince Harry and Meghan Markle – in pictures May 2019 A congratulatory banner message circling the BT Tower reading "Congratulations Harry and Meghan It's a Baby Boy!" AFP via Getty Prince Harry and Meghan Markle – in pictures May 2019 Footmen Stephen Kelly and Sarah Thompson set up an official notice on an easel at the gates of Buckingham Palace on May 6, announcing the birth of a son to Prince Harry, Duke of Sussex and Meghan, Duchess of Sussex AFP via Getty Prince Harry and Meghan Markle – in pictures May 2019 Pround parents pose with their newborn son Archie Harrison Mountbatten-Windsor in St George's Hall at Windsor Castle. The Duchess of Sussex gave birth at 5:26 on 6 May Getty Prince Harry and Meghan Markle – in pictures May 2019 Prince Harry and Meghan walk away after posing for photographs with their newborn son AFP via Getty Prince Harry and Meghan Markle – in pictures June 2019 Prince Harry and Meghan join the New York Yankees in their clubhouse and receive gifts for Archie ahead of their match against the Boston Red Sox at the London Stadium. The historic two-game series marked the sport's first games ever played in Europe and The Invictus Games Foundation was selected as the official charity of Mitel and MLB London Series 2019 Invictus Games Foundation/Getty Prince Harry and Meghan Markle – in pictures July 2019 Prince Harry and Meghan meet cast and crew, including US singer-songwriter Beyonce and her husband, US rapper Jay-Z as they attend the European premiere of the film The Lion King in London AFP via Getty Prince Harry and Meghan Markle – in pictures September 2019 The Duke and Duchess of Sussex dance as they arrive for a visit to the "Justice desk", an NGO in the township of Nyanga in Cape Town, as they begin their tour of the region. Their first official family visit in the coastal city AFP via Getty Prince Harry and Meghan Markle – in pictures September 2019 Prince Harry and Meghan pose with members of "Waves For Change" NGO at Monwabisi Beach outside of Cape Town. "Waves For Change" NGO fuses surfing with child-friendly mind and body therapy to provide mental health services to vulnerable young people living in challenging communities AFP via Getty Prince Harry and Meghan Markle – in pictures September 2019 The royals arrive to visit the oldest mosque of Cape Town in Dorp Street in Bo Kaap district AFP via Getty Prince Harry and Meghan Markle – in pictures September 2019 The Duchess of Sussex visits Auwal Mosque on Heritage Day with the Duke of Sussex during their royal tour of South Africa. Auwal Mosque is the first and oldest mosque in South Africa and for the Muslim community, this mosque symbolises the freedom of former slaves to worship Getty Prince Harry and Meghan Markle – in pictures September 2019 Prince Harry and Meghan hold their baby son Archie as they meet with Archbishop Desmond Tutu and his wife Leah at the Tutu Legacy Foundation in Cape Town AFP via Getty Prince Harry and Meghan Markle – in pictures September 2019 The British royal couple were on a 10-day tour of southern Africa -- their first official visit as a family since their son Archie was born AFP via Getty Prince Harry and Meghan Markle – in pictures October 2019 Prince Harry and Meghan meet Graca Machel, widow of the late Nelson Mandela in Johannesburg, South Africa. The Duke last met with Mrs Machel during his visit to South Africa in 2015 Getty Prince Harry and Meghan Markle – in pictures October 2019 Meghan and Prince Harry attend a roundtable discussion on gender equality with The Queens Commonwealth Trust (QCT) and One Young World at Windsor Castle Getty Prince Harry and Meghan Markle – in pictures December 2019 Prince Harry holding his son Archie. The photo was used on Instagram to wish their followers a happy new year SussexRoyal/PA Prince Harry and Meghan Markle – in pictures January 2020 Duke and Duchess of Sussex depart Canada House in London after visiting to show thanks for the warm hospitality and support they received during their recent stay in Canada Getty Prince Harry and Meghan Markle – in pictures January 2020 Front page headlines, from UK daily papers, reporting on the news that the Duke and Duchess of Sussex, plan to step back as "senior" members of the Royal Family AFP via Getty

Law firm Schillings, representing the duchess, said she had filed a High Court claim against the paper and its parent company Associated Newspapers over the alleged misuse of private information, infringement of copyright and breach of the Data Protection Act 2018.

A spokeswoman for the firm claimed the “intrusive” publication of the letter was part of the media group’s campaign to write “false and deliberately derogatory stories about her, as well as her husband”.

The legal proceedings in the Chancery Division of the High Court are being privately funded by Harry and Meghan.

Depending on the court ruling, proceeds from any damages will be donated to an anti-bullying charity.

The Schillings spokeswoman added: “Given the refusal of Associated Newspapers to resolve this issue satisfactorily, we have issued proceedings to redress this breach of privacy, infringement of copyright and the aforementioned media agenda.”

In his statement, Harry said he and Meghan believed in “media freedom and objective, truthful reporting” as a “cornerstone of democracy”.

However he added: “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.

“There is a human cost to this relentless propaganda, specifically when it is knowingly false and malicious, and though we have continued to put on a brave face – as so many of you can relate to – I cannot begin to describe how painful it has been.

“Because in today’s digital age, press fabrications are repurposed as truth across the globe. One day’s coverage is no longer tomorrow’s chip-paper.”

Harry said the couple, who are currently on a royal tour of South Africa, had been unable to correct “continual misrepresentations” in the press.

He said “positive” coverage of the tour exposed “the double standards of this specific press pack that has vilified her almost daily for the past nine months; they have been able to create lie after lie at her expense simply because she has not been visible while on maternity leave.

“She is the same woman she was a year ago on our wedding day, just as she is the same woman you’ve seen on this Africa tour.”

The duke added: “For these select media this is a game, and one that we have been unwilling to play from the start.

“I have been a silent witness to her private suffering for too long. To stand back and do nothing would be contrary to everything we believe in.”

Support free-thinking journalism and attend Independent events

He explained that the alleged unlawful publication of the private letter was done in “an intentionally destructive manner” to “manipulate” readers.

Harry claimed readers were misled by “strategically omitting select paragraphs, specific sentences, and even singular words to mask the lies they had perpetuated for over a year”.

He added: “There comes a point when the only thing to do is to stand up to this behaviour, because it destroys people and destroys lives.

“Put simply, it is bullying, which scares and silences people. We all know this isn’t acceptable, at any level.

“We won’t and can’t believe in a world where there is no accountability for this.”

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.”