The UK police force investigating Andrew Mountbatten-Windsor is thought to be examining an allegation he behaved inappropriately towards a woman at Royal Ascot.
The alleged incident at the racing festival attended by members of the Royal Family dates back to June 2002, according to a Sunday Times report.
It comes after Thames Valley Police made clear that it was examining sexual misconduct claims against the former prince as part of its wider probe into possible misconduct in public office.
Mountbatten-Windsor was arrested by the force in February over allegations he passed sensitive information to Jeffrey Epstein while serving as UK trade envoy.
The former prince, stripped of his titles over his ties to the late paedophile Jeffrey Epstein, was released under investigation and denied wrongdoing.
