The letter at the centre of the Duchess of Sussex’s legal battle with a British newspaper detailed her intimate “thoughts and feelings” about her father’s health and their relationship.

The duchess is bringing legal action against Associated Newspapers, publisher of the Mail on Sunday and MailOnline, over an article which reproduced parts of a handwritten letter she sent to her father Thomas Markle.

In court documents outlining her claim against the publisher, her solicitors say the letter was “obviously private correspondence” and she did not expect the contents to be made public.

Sections of the letter, which was sent to Mr Markle, 76, in August 2018, were published in February in the Mail on Sunday and on MailOnline.

The headline read: “Revealed: The letter showing true tragedy of Meghan’s rift with a father she says has ‘broken her heart into a million pieces’.”

In one extract, the duchess wrote: “Your actions have broken my heart into a million pieces – not simply because you have manufactured such unnecessary and unwarranted pain, but by making the choice to not tell the truth as you are puppeteered in this. Something I will never understand.”

Particulars of claim, prepared by Schillings law firm, on behalf of the duchess, say: “The letter was obviously private correspondence written by the claimant to her father.

“Further, it contained the claimant’s deepest and most private thoughts and feelings about her relationship with her father and were detailed by her at a time of great personal anguish and distress.

“The claimant intended the detailed contents of the letter to be private, and certainly did not expect them to be published to the world at large by a national newspaper, and without any warning.”

Associated Newspapers denies the allegations – particularly the claim that the letter was edited in any way that changed its meaning – and says it will contest the case.