Prince Andrew has been accused of "victim blaming" and "gaslighting" after his lawyers asked for Virginia Giuffre's mental health records - including confidential notes from her counselling sessions.
The Duke of York's legal team want to question Ms Giuffre's psychologist Dr Judith Lightfoot about her "alleged emotional and psychological harm and damages".
His lawyers have requested permission to inspect prescriptions written by Dr Lightfoot for Ms Giuffre - who has accused Andrew of sexual assault - as well as the expert's notes from their sessions together.
They also want to quiz the psychologist on the "theory of false memories" and ask her questions about Ms Giuffre's "alleged childhood trauma and abuse".
A source close to Prince Andrew told Sky News the duke's legal team is "perfectly entitled to test her claims".
'It's the lowest of the low'
Dr Charlotte Proudman, a barrister and Cambridge academic specialising in violence against women, said it appeared Andrew was trying to use Ms Giuffre's medical records to discredit her.
"It's nothing more than victim blaming and gaslighting," she told Sky News.
"Looking through her intimate, personal records when she would have told that person that information in the strictest confidence.
"For that to be used, manipulated and twisted against her is likely to be harmful and extremely damaging, and probably will be traumatising.
"It's another form of abuse but this time through the court process."
Dr Proudman said she hoped that Ms Giuffre opposed the request for details of her counselling sessions.
"It's a really low tactic," she added. "It's the lowest of the low."
The source close to the Duke of York said: "Ms Giuffre put her mental health at issue by suing for emotional distress damages.
"The duke's legal team are perfectly entitled to test her claims, determine her damages, if any, and see what she told her therapist or not."
Andrew's lawyers criticised request for proof of 'sweat claim'
Previously, Ms Giuffre's legal team had requested the duke provide proof he had a medical condition which meant he did not sweat.
The royal made the claim in his 2019 Newsnight interview after Ms Giuffre alleged he had been sweating heavily as they danced at a nightclub.
Andrew's lawyers reportedly said the request for evidence of his inability to sweat was "harassing" and sought confidential, private information, before adding: "No such documents exist in his possession."
Ms Giuffre, formerly known as Virginia Roberts, is suing Andrew in the US for allegedly sexually assaulting her when she was a teenager.
She claims she was trafficked by Andrew's friend Jeffrey Epstein, the convicted paedophile, to have sex with the duke when she was 17.
Andrew - who was stripped of his military titles this week - has vehemently denied the allegations against him.
'False memory' defence is 'go-to tactic'
After a judge rejected the royal's attempt to have the lawsuit thrown out, Andrew has claimed in court documents that Ms Giuffre, now 38, "may be suffering from false memories".
A "false memory" defence was used by Ghislaine Maxwell in her trial after her lawyers claimed the passage of time, alongside the intense media scrutiny of her case, had corrupted the memory of the accusers and witnesses.
Dr Proudman said it was "the go-to tactic of alleged and found perpetrators to allege that victims have misremembered things".
Maxwell was found guilty of recruiting underage girls to be sexually abused by her ex-boyfriend, Epstein, and will be sentenced in June.
Ahead of a civil trial planned for later this year, lawyers for Ms Giuffre have sought witness accounts from Andrew's former assistant Robert Olney and a woman called Shukri Walker, who claims to have seen the royal "with a young girl" in London's Tramp nightclub.
Ms Walker allegedly saw the royal "with a young girl around the time that (Ms Giuffre) contends Prince Andrew abused her in London after visiting Tramp Nightclub", court documents say.