Thames Valley Police are examining claims that Andrew Mountbatten-Windsor acted inappropriately towards a woman during Royal Ascot in 2002, it has emerged.
The alleged incident is reported to have occurred during the five-day racing festival in Berkshire, which the late Queen Elizabeth attended as part of her Golden Jubilee celebrations alongside other senior members of the Royal Family.
Mr Mountbatten-Windsor was pictured at the event with his daughter Princess Beatrice and the now King Charles.
Detectives are pursuing this matter as part of their wider investigation into misconduct in public office involving the former working royal.
Andrew Mountbatten-Windsor pictured at Ascot in 2002 beside then-Prince Charles
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It remains unclear whether the allegation was reported to authorities at the time or has only recently come to light.
A force spokeswoman stated this weekend: "We cannot go into specifics of our ongoing investigation, but we are following all reasonable lines of inquiry."
Mr Mountbatten-Windsor was taken into custody on his 66th birthday in February at his residence on the Sandringham estate in Norfolk, where he was held for 11 hours before being released under investigation.
He has consistently denied any wrongdoing.
Andrew Mountbatten-Windsor was also accompanied by his daughter, Princess Beatrice
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The late Virginia Giuffre's relatives have welcomed news that the Thames Valley inquiry will examine sexual misconduct allegations.
Her sister-in-law, Amanda Roberts, told Sky News: "It actually gives us hope. We are so thankful to Thames Valley police for taking this seriously."
Thames Valley Police are examining allegations including fraud, corruption, bullying and perverting the course of justice as part of their wider investigation into misconduct in public office involving the former working royal.
Assistant Chief Constable Oliver Wright of Thames Valley Police described the inquiry as complex, given the various forms misconduct in public office can take.
Andrew was arrested in February on suspicion of misconduct in public office and subsequently released on investigation | REUTERSLATEST ROYAL NEWS:
He appealed for anyone with relevant information to come forward, saying: "Whenever a victim-survivor is ready to engage with us, we're ready for you, at whatever point that may be."
Mr Mountbatten-Windsor was photographed on Saturday afternoon driving his Land Rover on the Sandringham estate after walking his dogs, marking his first public sighting since the expanded investigation was announced.
GB News has contacted Mr Mountbatten-Windsor for comment.