The King has given his backing for Buckingham Palace to assist the police investigation into Andrew Mountbatten-Windsor.
The monarch has authorised his officials to provide support needed to officers.
A Buckingham Palace spokesman added that King Charles had expressed “profound concern” over the claims against his younger brother and repeated his support for the victims of Jeffrey Epstein.
The King was heckled on Monday while on a royal engagement as pressure grew on the Royal family to compel Mr Mountbatten-Windsor to contribute to a police investigation.
The Prince and Princess of Wales made their first public comment about the Epstein files earlier on Monday, issued through their spokesman.
Thames Valley Police have confirmed they are examining allegations that Mr Mountbatten-Windsor shared confidential data with Epstein when the then Prince Andrew was working as a British trade envoy.
He has separately been accused of sexually assaulting Virginia Guiffre, which he denied, and with whom he settled in a civil claim, and of spending the night with an adult woman who was flown to the UK for sex with him.
Buckingham Palace has not yet been contacted by the police.
A palace spokesman said: “The King has made clear, in words and through unprecedented actions, his profound concern at allegations which continue to come to light in respect of Mr Mountbatten-Windsor’s conduct.
“While the specific claims in question are for Mr Mountbatten-Windsor to address, if we are approached by Thames Valley Police we stand ready to support them as you would expect. As was previously stated, Their Majesties’ thoughts and sympathies have been, and remain with, the victims of any and all forms of abuse.”
