In a statement, the monarch said: "I have learned with the deepest concern the news about Andrew Mountbatten-Windsor and suspicion of misconduct in public office. 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."
HELLO! understands that neither the King nor Buckingham Palace had been informed of the arrest before it happened.
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The King has previously stated that he stood "ready to support" the police into any investigation over his younger brother. A statement read: "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.
Charles said he was ready to "support" the police in any investigations
"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."
Andrew's arrest
Plain-clothed police officers were seen arriving at Sandringham, the King's private estate in Norfolk, in patrol cars just after 8am on Thursday. The former Prince is living at Wood Farm Cottage after the King evicted him from his home of 22 years, Royal Lodge, in Windsor.
Andrew is now in custody, as police carry out searches at addresses in Berkshire and Norfolk, Thames Valley police said.
8.00am: Police arrive at Wood Farm
Andrew Mountbatten-Windsor is arrested on suspicion of misconduct in public office on his 66th birthday. Around eight plain-clothed police officers arrive at Wood Farm on the King's private Sandringham estate just after 8am in six unmarked patrol cars. One officer carries a police-issue laptop. One car drives up the front drive while the other five enter through the back entrance to the five-bedroom farmhouse.
8.30am: Andrew escorted away
About 30 minutes later, an unmarked Norfolk police car leaves the premises. It is followed by another unmarked police car and a third vehicle containing the security team for Andrew. Range Rovers are seen driving away amid the arrest.
10.00am: Thames Valley Police releases statement
"As part of the investigation, we have today (19/2) arrested a man in his sixties from Norfolk 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. We will not be naming the arrested man, as per national guidance. Please also remember that this case is now active so care should be taken with any publication to avoid being in contempt of court."
Assistant Chief Constable Oliver Wright says: ''Following a thorough assessment, we have now opened an investigation into this allegation of misconduct in public office. 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.''
12.00pm: King Charles releases statement
''I have learned with the deepest concern the news about Andrew Mountbatten-Windsor and suspicion of misconduct in public office. 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. Charles R.''
Assistant Chief Constable Oliver Wright said: "Following a thorough assessment, we have now opened an investigation into this allegation of misconduct in public office. 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."
The King has not visited his disgraced brother, Andrew Mountbatten-Windsor, in Sandringham, despite Princess Anne and Prince Edward reportedly reaching out
Dame Charlotte Manley, 68, was Andrew's Private Secretary and Treasurer from 2001 to 2003 and accompanied him on trips abroad during his time as UK trade envoy