King Charles says “the law must take its course” after his brother former prince Andrew was arrested on suspicion of misconduct in public office.

British police arrived at Andrew Mountbatten-Windsor’s home at Wood Farm on the Sandringham estate on Thursday morning local time (9pm AEDT) with six unmarked police cars and about eight plain-clothed officers in attendance.

Thames Valley Police confirmed they arrested a man in his 60s on suspicion of misconduct in public office and are carrying out searches at addresses in Berkshire and Norfolk.

The man remains in police custody at this time, police said.

“Following a thorough assessment, we have now opened an investigation into this allegation of misconduct in public office,” Assistant Chief Constable Oliver Wright said.

“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.”

Thames Valley Police said earlier in February they were looking at allegations that Mountbatten-Windsor had passed confidential government documents to the late sex offender Jeffrey Epstein, according to recently released files.

Mountbatten-Windsor has denied any wrongdoing and said he regrets his friendship with Epstein, but he has not responded to specific requests for comment after the latest files were published by the US government.

It comes as Mountbatten-Windsor marks his 66th birthday on Thursday.\

Police arriving in Sandringham

(Source: 7NEWS)

Police arriving in Sandringham Images from the Epstein files appear to show Andrew Mountbatten Windsor crouching on all fours over a female lying on the floor. Credit: Deptartment of Justice/Department of Justice

King Charles released a statement on Thursday of his “deepest concern” of his brother’s arrest.

“I have learned with the deepest concern the news about Andrew Mountbatten-Windsor and suspicion of misconduct in public office,” the statement read.

“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.

“Let me state clearly: the law must take its course.

“As this process continues, it would not be right for me to comment further on this matter. Meanwhile, my family and I will continue in our duty and service to you all.”

Mountbatten-Windsor is the first senior British royal in modern history to be arrested.

The former prince is the brother of King Charles and the second son of the late Queen Elizabeth.

Mountbatten-Windsor had been reported to police by the anti-monarchy campaign group Republic following the release of more than three million pages of documents relating to Epstein, who was convicted of soliciting prostitution from a minor in 2008.

Those files suggested Mountbatten-Windsor had in 2010 forwarded to Epstein reports about Vietnam, Singapore and other places he had visited on official trips.

– With Reuters.