Buckingham Palace was handed emails six years ago that would have shown that Andrew Mountbatten-Windsor was sharing confidential government information while a trade envoy, according to court documents.
It has emerged that an archive of 30,000 emails, containing information about the former prince's controversial financial dealings, was given to the Lord Chamberlain, the most senior officer in the Royal Household, in 2020.
The emails had been taken from a personal business contact of the former Prince Andrew.
When asked about what happened to the emails, Buckingham Palace said: "Since there is an ongoing police enquiry concerning Mr Mountbatten-Windsor, it is not possible to provide any comment on these matters."
Last week, Thames Valley Police issued a fresh appeal for people to come forward with information, following Mountbatten-Windsor's arrest on suspicion of misconduct in public office.
But a search of court documents has revealed that a large cache of emails relating to Mountbatten-Windsor's finances had already been sent to Palace officials, years before the current inquiries began.
The emails had been the subject of a legal dispute and documents from a High Court judgment in April 2021 show that a "copy of the archive" had been provided for the "Lord Chamberlain in May 2020".
In June 2022, a subsequent High Court ruling refers to an email, dated 10 July 2020, saying the emails had been "delivered to Buckingham Palace".
This was after the then Duke of York had stepped down as a working royal, in the wake of his BBC Newsnight interview in November 2019.
The contents of the archive, with emails up to June 2013, are not fully known, but there have been glimpses of how relevant they could be.
Earlier this year, the Telegraph published emails showing Mountbatten-Windsor had requested a confidential briefing from Treasury officials in 2010 and then shared it with a personal business contact, giving it to him "before you make your move".
The briefing had been about problems in Iceland's banking industry - and the recipient had been Jonathan Rowland, whose father David Rowland had taken over the Luxembourg arm of a failed Icelandic bank, Kaupthing, which became Banque Havilland.
Jonathan Rowland previously confirmed to the BBC that these published messages about Icelandic banks had been taken from his account and were part of legal proceedings. It indicates that they would have been part of the archive later sent to the Palace.
And it was in those court battles over the alleged theft of the emails that it was revealed that copies had been given to the Palace.
The emails have a particular significance as they relate to a highly controversial time in Mountbatten-Windsor's financial dealings with the Rowlands and Banque Havilland, which later faced sanctions from regulators in the UK and the EU.
While it is not known what happened to the emails shared with the Palace, the release of the Epstein Files earlier this year in the US showed Mountbatten-Windsor's closeness to the Rowlands.
The Epstein files show Mountbatten-Windsor promoting their business ventures and gave personal assurances for David Rowland as his "trusted money man". Ex-wife Sarah Ferguson was also recorded as receiving a "Rowland bank loan".
According to court documents, the emails sent to the Palace had been taken from Jonathan Rowland's account after a dispute with a business colleague. They had then been obtained by a retail entrepreneur Kevin Stanford, former majority owner of All Saints, who had been in a separate dispute over investments in the Kaupthing bank.
Court documents say that Stanford offered the archive of emails to the authorities in Monaco and Luxembourg, and shared them with a number of people, including the Lord Chamberlain.
In 2020, the post of Lord Chamberlain was held by Lord Peel, whom the BBC has contacted, but Buckingham Palace has responded on his behalf. It's a role, according to the Royal Family website, which includes "overseeing the conduct and general business of the Royal Household".
The emails were given to the Palace during the reign of the late Queen Elizabeth II. There has been a tougher approach to Mountbatten-Windsor under the reign of King Charles, including taking away his titles. After Mountbatten-Windsor's arrest, a statement from the King said: "The law must take its course."
Mountbatten-Windsor has rejected any wrongdoing in his associations with Jeffrey Epstein and denied any personal gain from his role as trade envoy.
Stanford also shared some of the emails with a journalist, the judgment says. They are likely to have been the source for a number of newspaper stories about Andrew and his financial arrangements.
Author Andrew Lownie says there is still insufficient transparency in the UK about information relating to Mountbatten-Windsor and he's called for a parliamentary inquiry into his time as trade envoy.
He also says that Freedom of Information requests continue to be turned down and the "cover-up continues". Last month, he had sought information about a trip by Mountbatten-Windsor to Azerbaijan in 2011, but information was withheld by the Foreign Office on grounds including national security and law enforcement.
Thames Valley Police was asked whether it now had access to the 30,000 emails discussed in the High Court five years ago.
A spokesperson said they couldn't comment on specific information, but said: "We are aware of the allegations circulating in the public domain and encourage anyone with relevant information to get in touch."
A government spokesperson said: "We are fully cooperating with Thames Valley Police, and last week we published documents about the creation of the role and Andrew Mountbatten-Windsor's appointment in 2001."
Andrew Mountbatten-Windsor, Jonathan Rowland and Kevin Stanford were approached for comment.
