The Duchess of Sussex’s lawyer has claimed a former senior aide of the Prince of Wales could not have given evidence in Meghan’s copyright lawsuit against a newspaper publisher “without the authority of his bosses”.

Evidence from Jason Knauf, Harry and Meghan’s former communications secretary who at the time was a key aide of the then Duke and Duchess of Cambridge, was relied upon by Associated Newspapers Limited (ANL) as it appealed Meghan’s legal victory.

The duchess had successfully sued ANL, publisher of the Mail on Sunday and Mail Online, over five articles that reproduced parts of a “personal and private” letter to her estranged father Thomas Markle in August 2018.

A High Court judge ruled in Meghan’s favour last year without a full trial, but ANL appealed the decision and argued the case should go to a trial, with the publisher’s lawyers arguing new evidence from Mr Knauf suggested Meghan wrote the letter with the understanding that it could be leaked.

The challenge was dismissed by Court of Appeal judges.

Meghan’s lawyer Jenny Afia, a partner at Schillings Law Firm, speaking during the final episode of the Harry & Meghan Netflix documentary said: “When we were just about to go to the Court of Appeal, a senior member of the Duke of Cambridge’s team came forward to give this witness statement which wasn’t required and sadly there’s just no way he could have done that without the authority of his bosses.”

In separate documentary footage, the Sussexes are shown discussing the development at the time, with Meghan saying: “I know, it’s your brother, I’m not going to say anything about your brother, but it’s so obvious…”

Harry said there were attempts to try to “cover” the aide’s association with William, with Mr Knauf being labelled as a “former aide of Meghan and Harry” as opposed to, at the time, working as chief executive of William and Kate’s Royal Foundation.

An unidentified woman commented: “That’s what I keep saying… Why are we talking about him as her former aide and not the person who works for your brother?”

Harry replies: “That’s why I’m now living in a different country, because all the comms (communication) teams basically, like, try to outdo each other.

“This is the contract, the symbiotic relationship between the two institutions working the best that they can.”

Mr Knauf worked for the Sussexes as their communications secretary when in October 2018 he emailed bullying concerns about Meghan to William’s then private secretary, in an apparent attempt to force Buckingham Palace to protect staff. The claims have been previously denied by the duchess’ legal representatives.

The final episode of the Harry & Meghan Netflix documentary series featured a written response from both Mr Knauf and the duchess’ legal team.

The film stated: “In response to allegations that Mr Knauf submitted a voluntary witness statement in connection with the Daily Mail litigation with the consent of Prince William’s office, a representative for Mr Knauf sent the following statement:

“These claims are entirely false. Mr Knauf was asked to provide evidence by both the Duchess of Sussex and Associate Newspapers.

“He was advised by counsel that evidence in his possession could be relevant and he then provided this directly to the court, staying neutral in the process.”

The documentary added: “The Duchess of Sussex attorneys responded with the following statement:

“The legal team for Meghan, The Duchess of Sussex, disputes this claim. Mr Knauf was not asked to provide a witness statement by the duchess or her team.

“Nor do her attorneys believe Mr Knauf remained ‘neutral’ by submitting a witness statement relied on by Associated Newspapers whilst working for the Duke and Duchess of Cambridge.”