King Charles’ younger brother, Andrew Mountbatten-Windsor, was released from police custody Thursday evening after being arrested on suspicion of misconduct in public office over allegations that he passed confidential government documents to Jeffrey Epstein.

Mountbatten-Windsor, who turned 66 on Thursday, was questioned throughout the day by detectives from Thames Valley Police. Earlier this month, the force confirmed it was investigating claims that he shared sensitive documents with the late convicted sex offender while serving as a trade envoy.

The arrest of the senior royal, eighth in line to the throne, marks an extraordinary moment for the modern monarchy.

“I have learned with the deepest concern the news regarding Andrew Mountbatten-Windsor and the suspicion of misconduct in public office,” King Charles said in a statement.

A Reuters witness saw the former prince leave a police station in Aylsham, eastern England, shortly after 7:00 p.m. GMT, where he was met by a small group of photographers and television crews.