The Duke of York was allegedly paid £750,000 for “assistance” he provided “in relation” to an elderly Turkish woman’s passport, a judge overseeing a High Court dispute has been told.

Both the duke and his ex-wife Sarah have been named in a recent ruling on a row between Nebahat Isbilen, who is in her 70s, and Selman Turk.

In the ruling, deputy High Court judge David Halpern said he was told “substantial sums” were paid to Andrew and to Sarah, Duchess of York.

A document outlining Mrs Isbilen’s claim against Mr Turk, a Turkish businessman based in London, says she “authorised a transfer of £750,000” in late 2019.

The duke has since returned the money, the paper said.

Mrs Isbilen had needed help moving assets out of Turkey after her husband because a political prisoner, Judge Halpern was told.

Mr Turk, a former banker, agreed to help.

Mrs Isbilen alleges he “breached fiduciary obligations he owed to her” and advanced “claims in deceit”.

Mr Turk is fighting the case, which is ongoing and has been heard in London.

A number of preliminary rulings have been published.

Judge Halpern said a lawyer representing Mrs Isbilen told him in an affidavit that information had emerged to show evidence given by Mr Turk was “misleading”.

He said solicitor Jonathan Tickner told him evidence showed “money was used for purposes unconnected with Mrs Isbilen, e.g., substantial sums were paid to Prince Andrew, Duke of York, and to Sarah, Duchess of York”.

Judge Halpern said barrister Dan McCourt Fritz, who is leading Mrs Isbilen’s legal team, told him the “total sums which his client claims were misappropriated” amount to 50 million US dollars (about £38 million).

“Mr Turk has provided explanations for approximately two thirds of these sums, most of which have been allegedly spent on professional or other fees or lost in bad investments,” the judge added in his ruling.

“No explanation at all has been given for the remaining one third.”

A statement of claim drawn up by Mrs Isbilen’s lawyers said: “In or around November 2019, Mr Turk told Mrs Isbilen that she needed to make a purported ‘gift’ of £750,000 to HRH Duke of York by way of payment for assistance that he told her HRH Duke of York had provided in relation to Mrs Isbilen’s Turkish passport.

“The representation that Mrs Isbilen needed to make a gift to HRH Duke of York in connection with her passport (or for any other purpose) was false, and Mr Turk made it dishonestly, knowing it to be false and intending Mrs Isbilen to rely on it.”

The lawyers added: “Mrs Isbilen authorised a transfer of £750,000 … on 15 November 2019.”

They went on: “Mrs Isbilen has now received £750,000 from HRH Duke of York.”

Mr Tickner, head of fraud and commercial disputes at law firm Peters & Peters, told the PA news agency in a statement on Friday that Mrs Isbilen had trusted Mr Turk to help her through “extremely difficult” circumstances.

He added: “The court documents and decisions given in her case to date speak for themselves.”

A spokeswoman for the Duke said: “We are unable to comment on ongoing legal proceedings.”