Former prince Andrew Mountbatten-Windsor is back in the crosshairs of police in England ... he's under investigation for an alleged encounter back in the day with a woman at Royal Ascot.

Cops across the pond are reportedly looking into an alleged incident from 2002 at the famous racing festival ... with police "examining events in 2002 as they consider wider possible crimes by Andrew Mountbatten-Windsor, including sexual misconduct, ­corruption and fraud" ... according to The Sunday Times.

Royal Ascot is the most prestigious horse racing event in England with a rich history of tradition dating back centuries ... and in 2002, it was reportedly attended by Andrew's mom, Queen Elizabeth, his older brother the future King Charles, his younger brother Prince Edward, and his older daughter Princess Beatrice.

Thames Valley Police Department detectives are believed to be handling the investigation.

Unclear when the allegations from 2002 were reported to law enforcement ... but this is the first time we've heard of an investigation being launched.

It's been a rough year for Andrew ... as we reported, in February he was arrested on suspicion of sending confidential British trade reports to Jeffrey Epstein back in 2010.

Andrew's name and photos were plastered everywhere inside the voluminous Epstein Files ... including several chilling images where Andrew is seen kneeling over a woman while she's lying on the floor inside a room.

Following the Epstein Files release, King Charles stripped Andrew of his royal titles and booted him from the Royal Lodge residence in Windsor.