Andrew Mountbatten-Windsor is under investigation following allegations that he behaved inappropriately towards a waitress during Royal Ascot in 2002, according to reports emerging over the weekend.
Thames Valley Police is examining the claims as part of its broader inquiry into the 66-year-old former working royal.
The alleged incident occurred during the prestigious Berkshire racing festival, which that year coincided with Queen Elizabeth II's Golden Jubilee celebrations.
Records indicate Mr Mountbatten-Windsor was present for at least two days of the five-day event, where he was photographed alongside his brothers, the now King Charles and Prince Edward.
Andrew is being investigated over his alleged behaviour towards a waitress at Royal Ascot
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A Thames Valley Police spokesperson stated: "We cannot go into specifics of our ongoing investigation, but we are following all reasonable lines of inquiry."
The investigation forms part of a wider probe into potential misconduct in public office during Mr Mountbatten-Windsor's decade-long role as a Government trade envoy between 2001 and 2011.
On his 66th birthday in February, Mr Mountbatten-Windsor was arrested at his residence on the Sandringham estate in Norfolk on suspicion of misconduct in public office.
He spent 11 hours in police custody before being released under investigation.
Andrew Mountbatten-Windsor pictured at Ascot in 2002 beside then-Prince Charles | GETTYThe arrest followed the release of documents by the US Justice Department as part of its inquiry into the late sex offender Jeffrey Epstein, with files raising questions as to whether Mr Mountbatten-Windsor may have shared confidential Government reports with the disgraced financier.
Earlier this month, Thames Valley Police disclosed that its inquiry expanded significantly beyond the original scope, now encompassing potential sexual offences and corruption allegations.
Officers confirmed that any fresh evidence uncovered could either be incorporated into the existing misconduct investigation or pursued as separate criminal matters.
Buckingham Palace declined to offer any statement regarding the allegations, citing the active police investigation.
Andrew Mountbatten-Windsor was also accompanied by his daughter, Princess Beatrice | GETTYLATEST ROYAL NEWS:
"Since there is an ongoing police inquiry concerning Mr Mountbatten-Windsor, it is not possible to provide any comment on these matters," a Palace spokesman said.
King Charles has previously indicated his willingness to cooperate fully with the police investigation into his younger brother.
Mr Mountbatten-Windsor maintains his innocence and has consistently denied all allegations of wrongdoing levelled against him.
Ascot Racecourse also declined to comment publicly, but has previously vehemently denied all wrongdoing. It is understood that the venue would assist the police if requested to do so.