Andrew Mountbatten-Windsor was arrested at approximately 08:00 on Thursday, according to reports from the BBC.
The arrest was related to information that emerged from the massive Epstein file release in January, specifically regarding activities while Andrew was a trade envoy for the British government.
Thames Valley Police became involved after reviewing emails between Andrew and the late sex offender Jeffrey Epstein, as revealed in the Epstein files.
Investigation Background
One email, dated November 2010, showed Andrew forwarding country reports to Epstein just five minutes after receiving them, despite Epstein's prior conviction for sex offenses.
Further email revelations included a confidential briefing on investment opportunities in Afghanistan's Helmand Province, sent by Andrew to Epstein on Christmas Eve 2010.
Police Response
Thames Valley Police will have relied on more than just the emails that have been made public to build a case, having requested additional emails from the government and the palace.
The palace stated last Monday that it would "support" Thames Valley Police in their investigation.
Next Steps
Andrew has been released under investigation, which does not rule out further questioning at a later date.
Detectives will now review the evidence and decide whether to charge Andrew, in consultation with lawyers from the Crown Prosecution Service.
