The Duchess of Sussex was helped to write a letter at the centre of a legal case by palace aides, court documents allege.

Meghan is suing Associated Newspapers Ltd (ANL), publisher of the Mail on Sunday and MailOnline, over an article which reproduced parts of the handwritten letter sent to her estranged father Thomas Markle in August 2018.

Documents lodged with the High Court by ANL claim Jason Knauf “and/or” the Kensington Palace communications team “contributed” to a draft of the document.

At the time, Mr Knauf was the Duke of Sussex’s communications secretary and, after holding the same post with the Duke and Duchess of Cambridge, is now chief executive of William and Kate’s Royal Foundation.

The duchess, 39, claims the February 2019 publication of parts of the letter to her 76-year-old father was a misuse of her private information and breached the Data Protection Act, as well as a breach of her copyright.

ANL’s legal team says in its document: “It is for the claimant to prove she was the only person who contributed to the writing of the electronic draft.

“Without prejudice to the generality of the foregoing, the defendant infers that Jason Knauf and/or others in the Kensington Palace Communications team contributed to the writing of the electronic draft.”

The lawyers claim the duchess’s letter is not her “intellectual creation” and therefore not original work, as it was copied from an electronic draft, had the input of the communications team and contained pre-existing facts including Meghan’s “view of her father and his conduct”, and so was not subject to copyright protection.

The start of the duchess’s High Court case against ANL has been delayed from the new year until autumn 2021 because of a “confidential reason”.

But the court will hear a summary judgment application in January, when Meghan’s lawyers will argue that ANL’s defence has no prospect of succeeding at a trial.

The duchess is seeking damages from ANL for alleged misuse of private information, copyright infringement and breach of the Data Protection Act.

ANL wholly denies the allegations, particularly the duchess’s claim the letter was edited in any way that changed its meaning, and says it will hotly contest the case.

Meghan is suing Associated Newspapers over five articles, two in the Mail on Sunday and three on MailOnline, which were published in February 2019.