Andrew Mountbatten-Windsor was arrested on Thursday on "suspicion of misconduct in public office" during his time as UK trade envoy, police said.
A statement released on Thursday morning did not name the former British royal, but said searches are being carried out at "at addresses in Berkshire and Norfolk", while a man in his sixties "remains in police custody". Mountbatten-Windsor turned 66 on Thursday.
“It is important that we protect the integrity and objectivity of our investigation as we work with our partners to investigate this alleged offence," the statement said.
“We understand the significant public interest in this case, and we will provide updates at the appropriate time,” it added.
Mountbatten-Windsor's brother and Britain's King Charles III issued a statement following the news of his arrest, saying that "what now follows is the full, fair and proper process by which this issue is investigated in the appropriate manner and by the appropriate authorities."
"In this, as I have said before, they have our full and wholehearted support and co-operation," King Charles III said. "Let me state clearly: the law must take its course."
Unmarked police cars were seen earlier on Thursday morning at Sandringham in Norfolk, where he has been living since leaving his home in Windsor.
New revelations last week appeared to show Mountbatten-Windsor sent disgraced financier and convicted sex offender Jeffrey Epstein potentially confidential documents during his time as a UK trade envoy.
Royal family 'concerned'
Thames Valley Police, west of London, confirmed earlier this month that it was "assessing" misconduct in public office accusations against the former prince.
It prompted King Charles III to voice "concern" over the actions of his brother and issue an unprecedented statement noting Buckingham Palace was "ready to support" the police in their assessment.
In the latest potentially damaging disclosure, the Financial Times reported Tuesday that emails show Andrew agreed to help negotiate an $8-billion cash-for-oil swap involving two foreign entities.
The ex-royal and a banker with whom he worked closely exchanged multiple messages about the plan with Epstein, starting while the financier was still under house arrest for a 2008 conviction for soliciting sex from an underage girl, according to the newspaper.
In October, King Charles III stripped Mountbatten-Windsor of his royal titles and ordered him to vacate Royal Lodge, his residence in the grounds of Windsor Castle.
The decision followed years of controversy over Mountbatten-Windsor's association with Epstein. He stepped back from royal duties in 2019 after a disastrous BBC interview about his friendship with Epstein.
Mountbatten-Windsor has not been charged with any crimes in connection with Epstein and has repeatedly denied any wrongdoing.
In 2022, then-Prince Andrew paid a settlement to Virginia Giuffre, who accused him of sexually abusing her when she was 17 years old. The settlement amount was not disclosed, though reports estimated it at between £7.5 million and £12 million.
While he did not admit wrongdoing, Mountbatten-Windsor acknowledged Giuffre's suffering as a victim of sex trafficking in a joint statement announcing the settlement.
Mountbatten-Windsor said he had not remembered meeting Giuffre, despite a photograph showing him with his arm around her waist alongside Maxwell.
Giuffre died by suicide in April at the age of 41 at her farm in Western Australia. Her posthumous memoir Nobody's Girl was published in October.
