The Duchess of Sussex’s former communications secretary “led extensive efforts” to defend her reputation and “protect her father from media intrusion”, according to a letter sent to the Mail On Sunday’s lawyers.

Jason Knauf “repeatedly” spoke to Meghan’s estranged father Thomas Markle and directly contacted media organisations to “object to intrusions into Mr Markle’s privacy” from 2016, his lawyers said in a letter last month.

Mr Knauf also advised that “a reference to Mr Markle’s ill-health be included” in a letter sent by the duchess to her father in August 2018, which his solicitors described as “only a very minor suggestion”.

But Mr Knauf “did not suggest any specific wording” and “did not draft, and has never claimed to have drafted, any parts of” the letter to Mr Markle, his lawyers Addleshaw Goddard said in a letter obtained by the PA news agency.

Mr Knauf, who now works as the chief executive of the Royal Foundation of the Duke and Duchess of Cambridge, has been dragged into his former employer’s High Court battle with the publisher of the Mail On Sunday.

Meghan, 39, sued Associated Newspapers Limited (ANL), which is also the publisher of MailOnline, over a series of articles which reproduced parts of a “personal and private” letter to Mr Markle, 76.

She claimed the five articles, published in print and online in February 2019, misused her private information, infringed her copyright and breached the Data Protection Act.

In February, the High Court granted Meghan summary judgment in relation to her privacy claim, meaning she won that part of the case without having to go to trial, as well as most of her copyright claim.

This week, Lord Justice Warby also granted summary judgment in relation to the remaining parts of the duchess’s copyright claim.

ANL previously said it believed Mr Knauf was a co-author of the letter and the publisher argued that meant that the letter belonged to the Crown.

But lawyers acting on behalf of the Queen said any copyright in the letter does not belong to the Crown, the High Court heard on Wednesday.

Solicitors representing “the Keeper of the Privy Purse, acting on behalf of Her Majesty the Queen” told Meghan’s solicitors they “did not consider the Crown to be the copyright owner”.

Mr Knauf “emphatically” denied being a co-author, the court was told, with his lawyers telling ANL “it has never been his belief that he was an author”.

In the letter to ANL’s solicitors, released to the media in full on Thursday, Mr Knauf’s lawyers said: “Mr Knauf did not draft, and has never claimed to have drafted, any parts of the electronic draft or the letter and would never have asserted copyright over any of their content.

“In our client’s view, it was the duchess’s letter alone.

“From 2016, Mr Knauf led extensive efforts to protect the privacy and reputation of the duchess and, as and when directed by her, the privacy of her parents.

“This included drafting a press statement in November 2016, issued in his own name, condemning racist and sexist coverage of Ms Markle, as she then was, and other regular interventions – directly to media and through the Independent Press Standards Organisation (Ipso) – to request privacy both for her and for her parents.”

Mr Knauf was “involved in providing advice and offering support with a view to protecting her father from media intrusion”, including “many conversations with Mr Markle and a number of interventions, through Ipso and directly with publications, to object to intrusions into Mr Markle’s privacy”, the letter said.

This support continued “even after the Mail On Sunday reported that Mr Markle had allegedly been co-operating with press photographers” shortly before the Duke and Duchess of Sussex’s wedding, the letter added.

“Mr Knauf and his colleagues made significant efforts over many months to protect Mr Markle and to object to intrusions into his privacy, in addition to the steps that were regularly taken to object to coverage of the duchess herself, where this was perceived to be unfair or untrue,” it continued.

Addleshaw Goddard told ANL that Meghan sent Mr Knauf “a series of text messages in August 2018” about a draft of the letter to her father, which she composed on her mobile phone before transcribing it by hand.

Their letter added: “Given that Mr Knauf was a trusted adviser who had spoken to Mr Markle repeatedly and supported the duchess by trying to protect her father from media intrusion, there was nothing unusual about her asking for his opinion on the electronic draft.

“Mr Knauf made only a very minor suggestion on the text of the letter, namely that a reference to Mr Markle’s ill-health be included.

“This advice was accepted, but Mr Knauf did not suggest any specific wording.”

Ian Mill QC, representing the duchess, told the High Court on Wednesday: “This unequivocal statement of Mr Knauf’s position also gives the lie to the defendant’s inferential case, in its defence to both the privacy and copyright claims, that the claimant considered using the letter ‘as part of a media strategy’.”

In February, Lord Justice Warby said ANL’s publication of Meghan’s letter to her father was “manifestly excessive and hence unlawful”.

He said: “It was, in short, a personal and private letter.

“The majority of what was published was about the claimant’s own behaviour, her feelings of anguish about her father’s behaviour, as she saw it, and the resulting rift between them.

“These are inherently private and personal matters.”

The judge said “the only tenable justification for any such interference was to correct some inaccuracies about the letter”, contained in an article in People magazine, published days before ANL’s five articles, which featured an interview with five friends of Meghan.

But Lord Justice Warby added: “The inescapable conclusion is that, save to the very limited extent I have identified, the disclosures made were not a necessary or proportionate means of serving that purpose.

“For the most part they did not serve that purpose at all.

“Taken as a whole, the disclosures were manifestly excessive and hence unlawful.”

In March, the publisher was ordered to print a statement on the front page of the Mail On Sunday and a notice on page three of the paper stating it “infringed her copyright” by publishing parts of the letter to Mr Markle.

But the front-page statement about Meghan’s victory in her copyright claim is on hold, to allow ANL time to seek permission to appeal.