The Supreme Court in London has ruled that letters sent by Prince Charles to ministers can be disclosed to the media. Prime Minister David Cameron has described the judgment as "disappointing."
A ruling by Britain's Supreme Court on Thursday will allow the media to publish previously unseen letters written by Prince Charles to ministers in 2004-2005.
The judgment follows a long legal battle by UK daily broadsheet The Guardian to gain access to the letters.
The ruling has also raised concerns over the future king's political neutrality.
The Guardian newspaper fought for a decade to obtain the letters sent to ministers under then-Prime Minister Tony Blair.
However, successive governments acted to prevent their publication for fear of undermining the position of the heir to the throne.
Prime Minister David Cameron described the Supreme Court judgment as "disappointing" and said the government would now consider how to release the details.
"This is about the principle that senior members of the royal family are able to express their views to government confidentially. I think most people would agree this is fair enough," said Cameron.
A spokesperson for Prince Charles at Clarence House, his official London residence, echoed Cameron's sentiments: "Clarence House is disappointed the principle of privacy has not been upheld."
Political neutrality under scrutiny
The royal family is supposed to remain politically neutral under Britain's unwritten constitution.
Queen Elizabeth II has kept her opinions to herself during her 63-year reign, but Charles has expressed views on issues including nature conservation and architecture.
The letters, known as the "black spider memos" due to his scrawled handwriting, are potentially controversial if they show he disagreed with ministers and tried to influence policies.
Privacy battle in public
Then-Attorney General Dominic Grieve, who called the letters "particularly frank," used his ministerial veto in 2012 to block their disclosure.
However, the veto was declared unlawful by the Court of Appeal last year.
In a final effort to stop disclosure, Grieve went to the Supreme Court, but the appeal was dismissed.
Alan Rusbridger, editor-in-chief of the Guardian, said he was "delighted" about the ruling.
"The government wasted hundreds of thousands of pounds trying to cover up these letters, admitting their publication would 'seriously damage' perceptions of the prince's political neutrality. Now they must publish them so that the public can make their own judgment," he said in a statement.
Cameron hinted the law could change again as a result of Thursday's ruling.
"Our freedom of information laws specifically include the option of a governmental veto, which we exercised in this case for a reason. If the legislation does not make parliament's intentions for the veto clear enough, then we will need to make it clearer," he said.