Prince Andrew's lawyers will be able to access a settlement agreement reached between his accuser and Jeffrey Epstein which the Duke's legal team believe could nullify the civil sexual assault case against him.
Andrew B Brettler, who represents the Duke of York, had argued at a previous hearing that Virginia Giuffre - who is suing the Queen's son for alleged sexual assault - had entered into a "settlement agreement" which would end her current lawsuit.
Ms Giuffre's lawyer David Boies was on Wednesday granted permission by Judge Loretta Preska to supply the Duke's legal team with the previously sealed document, but the attorney believes it is "irrelevant to the case against Prince Andrew".
During the first pre-trial hearing of the case last month, the Duke's lawyer said: "There has been a settlement agreement that the plaintiff has entered into in a prior action that releases the Duke and others from any and all potential liability."
Mr Brettler was referring to the 2009 settlement between Ms Giuffre and convicted sex offender Jeffrey Epstein of a Florida state case to which the Duke was not a party.
Ms Giuffre is suing the Duke for allegedly sexually assaulting her when she was a teenager. She claims she was trafficked by Epstein, the Duke's former friend, to have sex with the Duke when she was aged 17 and a minor under US law.
The Duke has denied all the allegations.
It came as it emerged that Sarah, Duchess of York, will avoid questions about the Duke at a promotional book festival event on Thursday, after Henley Literary Festival asked its audience to submit questions for the Duchess in advance.
A source said: "She doesn't shy away from questions on any subject, but this is a literary festival and the publishers are keen to keep the focus on the book."