Andrew Mountbatten Windsor has launched legal action against Thames Valley Police, contesting the lawfulness of search warrants executed during his February arrest linked to the Jeffrey Epstein investigation.
The former Duke of York filed a judicial review concerning searches at his Sandringham Estate home and his former Royal Lodge residence in Windsor.
This marks the first time a British royal family member has challenged criminal proceedings since 1649.
Authorities detained him on suspicion of misconduct in public office after documents suggested he shared sensitive trade information with Epstein between 2001 and 2011.
Detectives questioned Mountbatten Windsor for nearly 12 hours before releasing him under investigation.
Subsequent searches at Marsh Farm and Royal Lodge led to the seizure of documents, though US authorities have not handed over unredacted files requested by UK investigators.
A High Court judge granted permission for the judicial review application earlier this year.
A private High Court hearing scheduled for later this week will determine whether specific court documents regarding the legal challenge can be made public.
Buckingham Palace previously stated that the monarch received no advance notice of the arrest before the initial detention occurred in February.
"The law must take its course," said King Charles III.
The monarch further addressed the ongoing police proceedings at the time of the arrest.
"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," said King Charles III.
The king also confirmed the royal family's stance regarding the law enforcement investigation.
"In this, as I have said before, they have our full and wholehearted support and co-operation," said King Charles III.
Thames Valley Police expanded its scope in May to solicit details on separate allegations of sexual misconduct, while Mountbatten Windsor remains under investigation.
