A UK newspaper group began a legal challenge on Tuesday over a ruling that it breached the Duchess of Sussex's privacy by publishing parts of a letter she wrote to her estranged father.

Meghan, 40, successfully sued Associated Newspapers Limited, which publishes the Daily Mail, MailOnline and Mail on Sunday, over a series of articles based on the letter to Thomas Markle.

A judge at the High Court in February said the handwritten letter was "personal and private" and publication was "manifestly excessive and hence unlawful" and ordered it to print a front-page statement acknowledging her victory.

But at the start of the case before three appeal court judges Tuesday, lawyers for the publishers submitted the letter was written knowing that it may be made public.

"We read the judgment as implicity accepting that the letter was crafted as an intimate communication for her father's eye's only," said Andrew Caldecott.

But he said that was "false" based on new evidence.

"The letter was crafted specifically with the potential of public consumption in mind because the claimant appreciated Mr Markle might disclose it to the media," he added.

The lawyer pointed to an interview which five of her friends gave to the US magazine People, which her father considered to be "a serious attack on him".

Meghan "made no effort to correct" it, he added. At the original hearing, Associated argued its articles were intended to correct inaccuracies in the People interview.

Caledcott said Meghan's father had a right to reply and that she had no "reasonable expectation of privacy of the text of the letter", as it had already been widely reported.

The case, which is due to last up to three days with judgment given at a later date, is the latest in the former television actress's long-running battle with Associated.

The newspaper group has not yet published the front-page statement acknowledging her privacy win because of the appeal.

As well as the privacy claim, the former television actress successfully sued for breach of copyright and data protection infringement.

The letter to Thomas Markle, 77, was written a few months after her wedding to Queen Elizabeth II's 37-year-old grandson, Prince Harry.

It asked him to stop talking to tabloid newspapers and making false claims about her in interviews.

Meghan and Harry have waged a high-profile war against the media, blaming intrusion for their decision to quit royal life last year and move to the United States.

But they have since attracted criticism for launching themselves into the public eye, with a series of lucrative deals with firms including Spotify, Netflix and Apple TV+.