Hillary Clinton has called for Andrew Mountbatten-Windsor to appear before US Congress regarding his connections to Jeffrey Epstein.
The former US Secretary of State, who herself will be testifying in the probe, said on Monday: "I think everyone should testify who was asked to testify.
"I just want it to be fair. I want everyone treated the same way," she told the BBC.
Mrs Clinton and her husband, ex-President Bill Clinton, have confirmed they will give evidence to the congressional inquiry into Epstein next week.
Their decision to cooperate means the couple will avoid being held in criminal contempt of Congress.
The Republican-controlled House of Representatives had been preparing to vote on contempt charges, which could have seen the couple risk jail time, after they ignored legal summonses.
The former President's deputy chief of staff confirmed on social media some weeks ago that the couple "will be there".
Bill Clinton's appearance will be a historic occasion - no former US president has testified before a congressional committee since Gerald Ford did so in 1983.
At the Munich Security Conference on Saturday, Mrs Clinton renewed her demands for the complete release of the Epstein files.
"It is something that needs to be totally transparent," she said. "I've called for many, many years for everything to be put out there so people can not only see what's in [the files] but also, if appropriate, hold people accountable. We'll see what happens."
Hillary Clinton has called for Andrew Mountbatten-Windsor to appear before US Congress
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The files contain images of her husband swimming with Ghislaine Maxwell and an unidentified individual in a hot tub.
Sir Keir Starmer suggested last month that Andrew would be letting down victims if he withheld any relevant information.
US Vice-President JD Vance has also urged Andrew to testify before Congress.
While back in Britain, former Business Secretary Sir Vince Cable on Sunday demanded an investigation into Andrew's tenure as UK trade envoy for potential corruption.
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Both Bill and Hillary Clinton could have risked jail over a contempt resolution - but went on to agree to testify
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Sir Vince's time in Cabinet between 2010 and 2015 overlapped with Andrew's position.
He described the alleged activity as "totally unacceptable".
"We need a police or DPP (Director of Public Prosecutions) check on whether criminal corruption took place and a government investigation into how this was allowed to happen," he said.
Ex-Business Secretary Sir Vince Cable on Sunday demanded an investigation into Andrew's tenure as UK trade envoy
| GETTYThames Valley Police have confirmed they are in discussions with Crown Prosecution Service specialists over the allegations against Andrew - all of which he denies.
The force said on Wednesday that it could not provide timescales for when a decision on opening a criminal investigation would be made.
However, it assured the public that progress was being made as quickly as possible.
Assistant Chief Constable Oliver Wright said the force was leading the assessment of allegations relating to misconduct in public office.
These allegations specifically concern documents within the US Department of Justice's Epstein files.