Andrew Mountbatten-Windsor has been arrested on suspicion of misconduct in public office and is in police custody.
Thames Valley Police confirmed the arrest on Thursday following allegations made against the former prince after the release of millions of pages of files related to paedophile financier Jeffrey Epstein.
Andrew is the first senior royal in modern history to be arrested.
The news comes as pictures circulated online appearing to show unmarked police cars attending Wood Farm on the Sandringham Estate in Norfolk, with plain-clothed officers appearing to gather outside Andrew’s home on his 66th birthday.
Thames Valley Police previously said the force was reviewing allegations that a woman was trafficked to the UK by Jeffrey Epstein to have a sexual encounter with Andrew, and claims he shared sensitive information with the paedophile while serving as the UK’s trade envoy.
Searches are being carried out at addresses in Berkshire and Norfolk, the force said.
Emails released by the US Department of Justice appeared to show the former duke sharing reports of official visits to Hong Kong, Vietnam and Singapore.
One email, dated November 2010, appeared to be forwarded by Andrew five minutes after being sent by his then-special adviser Amir Patel.
Another, on Christmas Eve 2010, appeared to send Epstein a confidential brief on investment opportunities in the reconstruction of Helmand Province, Afghanistan.
Assistant Chief Constable Oliver Wright said: “Following a thorough assessment, we have now opened an investigation into this allegation of misconduct in public office.
“It is important that we protect the integrity and objectivity of our investigation as we work with our partners to investigate this alleged offence.
“We understand the significant public interest in this case, and we will provide updates at the appropriate time.”
Andrew’s arrest comes days after Buckingham Palace said it would “stand ready to support” the police if approached over the claims made against him.
A spokesman for the Palace added that the King had made clear his “profound concern” over Andrew’s alleged conduct.
The King’s brother is effectively no longer a royal, becoming a commoner after he was stripped by the monarch of both his right to be a prince and his dukedom late last year over his association with Epstein.
He does, however, remain in the line of succession – he is eighth in line to the throne, having gradually moved down after being born second in line.
