The former prince was arrested on Thursday morning, Thames Valley Police said.
Andrew Mountbatten-Windsor remains in police custody after being arrested on suspicion of misconduct in public office over his ties to paedophile financier Jeffrey Epstein.
The former prince, who became the first senior royal in modern history to be arrested, is accused of sharing sensitive information with Epstein while serving as the UK’s trade envoy.
His brother, the King, said “the law must take its course” after expressing his “deepest concern” over the arrest, which came after millions of files were released by the US Department of Justice in relation to the Epstein scandal.
Thames Valley Police previously said the force was reviewing allegations after emails released as part of the trove of documents appeared to show the former duke sharing reports of official visits to Hong Kong, Vietnam and Singapore with the disgraced financier.
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 show Andrew send Epstein a confidential brief on investment opportunities in the reconstruction of Helmand province, Afghanistan.
Andrew’s arrest on Thursday, on his 66th birthday, followed pictures of officers in attendance at his home on the Sandringham estate in Norfolk – with police seen gathering outside Wood Farm.
In the afternoon, several police officers were stood nearby, close to a private entrance to the estate.
Searches have also taken place at the Royal Lodge, Andrew’s former home in Windsor, Berkshire, where multiple vans carrying uniformed officers arrived on Thursday afternoon.
Andrew has denied any wrongdoing over his Epstein links, but has not directly responded to the latest allegations.
It is understood neither the King nor Buckingham Palace was informed in advance of the arrest.
The Prince and Princess of Wales are understood to support the King’s statement, which read: “As I have said before, they (the police) have our full and wholehearted support and co-operation.
“Let me state clearly: the law must take its course.”
The King carried on with his duties as monarch in the wake of Andrew’s arrest by continuing with his planned ambassadorial in-person audiences in the Throne Room at St James’s Palace.
He was later met with questions about his brother while arriving at an engagement in the Strand area of central London, hours after issuing his statement.
Charles did not respond to questions.
The Queen also did not respond after being asked “are you concerned about Andrew’s arrest, your majesty?” during an engagement in Westminster.
According to the Crown Prosecution Service’s (CPS) website, misconduct in public office carries a maximum sentence of life imprisonment.
A suspect can generally be held in custody for up to 24 hours, but this can be extended to 96 hours if an extension is sought at a magistrates’ court.
When the custody time limit has expired, the majority of suspects are either charged or released pending further investigation.
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.
A number of police forces across the UK are assessing information released as part of the Epstein files document dump.
Officers from Surrey, Bedfordshire, Essex, Norfolk, the West Midlands, Wiltshire and Scotland have all said they are reviewing information.
On Wednesday, the Met said it was also looking at allegations Andrew’s protection officers turned a “blind eye” to his visits to Epstein’s island, Little St James.
The National Crime Agency said it was supporting UK forces in their Epstein files probes.
