Meghan Markle and husband Prince Harry are suing British Sunday newspaper, Mail on Sunday, over a claim that the paper unlawfully published one of her private letters. 

Prince Harry said in a statement that the Duke and Duchess of Sussex have opened legal proceedings as a response to what he called "bullying" by the British press. 

"My deepest fear is history repeating itself. I've seen what happens when someone I love is commoditized 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," he said. 

Schillings, the law firm representing the Duke and Duchess, said the "unlawful" publication of private letters was part of "campaign by this media group to publish false and deliberately derogatory stories about her, as well as her husband."

Prince Harry also said the newspaper had "purposely misled (readers) by strategically omitting select paragraphs, specific sentences, and even singular words."

The Mail on Sunday have denied the claim.

"The Mail on Sunday stands by the story it published and will be defending this case vigorously," said a spokesperson. "Specifically, we categorically deny that the Duchess' letter was edited in any way that changed its meaning."

Schillings have also stated that the lawsuit was being paid for privately by the Sussexes. 

The law firm has filed a claim against the paper and parent company, Associated Newspapers, for alleged misuse of private information, infringement of copyright and breach of the Data Protection Act 2018.

In the UK, among other countries, copyright law protects all 'literary works' when they become available in a physical form. This means that the contents of a letter is owned by the 'first author' and protected by copyright. The actual physical letter is owned by the person to whom it was sent. 

The copyright lasts for the author's entire life, plus 70 years – typically this is passed down with their estate when they pass away. 

With input from Reuters