Britain's top court has ruled secret letters from Prince Charles to government ministries should be published, in a potential setback for the monarchy seen as a victory for media freedoms.
"The Supreme Court dismisses the attorney-general's appeal," read the ruling, after the government went to court to prevent the publication of secret letters believed to show Prince Charles interfering in politics.
The ruling was immediately praised by The Guardian newspaper, which had brought the case to court, but criticised by the prince's official residence, Clarence House, and prime minister David Cameron.
"Clarence House is disappointed the principle of privacy has not been upheld," a spokesman said.
The long-running case relates to 27 items of correspondence sent in 2004 and 2005 by the Prince, who is known for his outspoken views on the environment and energetic activism on social issues.
The letters were sent to seven government departments and the previous attorney-general, who stopped their publication on the basis that they reflected the prince's "most deeply held personal views and beliefs".
There is concern that their publication could harm the royal family's image of political neutrality in a country where the monarch "reigns but does not rule".
Guardian editor Alan Rusbridger hailed the ruling as the result of a "brilliant 10-year campaign" to ensure the letters were made public.
"Guardian wins," he wrote on Twitter.
In a statement, Mr Rusbridger said: "This is a good day for transparency in government and shows how essential it is to have a fully independent judiciary and free press."
The letters have been dubbed the "Black Spider Memos", due to Charles's spiky handwriting.
No date has been fixed for their publication, although the BBC reported that the government now has 30 days to release them.
"This is a disappointing judgement and we will now consider how to release these letters," prime minister David Cameron said in a statement.
"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."
Letters to 'change public perception of the monarchy'
The government had vetoed the release of the letters under Freedom of Information laws, but this has now been struck down by the courts.
Mr Cameron said the government would consider amending the law for future cases, although that cannot happen before elections in May as parliament's last day before the vote was on Thursday.
"If the legislation does not make parliament's intentions for the veto clear enough, then we will need to make it clearer," Mr Cameron said.
A new biography of Prince Charles last year reignited debate about whether he is fit to become king.
Catherine Mayer's "Charles: The Heart of a King" portrays a royal household riven with infighting, and an heir to the throne uncomfortable with the distant impartiality that has been the hallmark of his mother Queen Elizabeth II's reign.
The 66-year-old Prince of Wales, Queen Elizabeth's eldest son, has spent a lifetime in preparation for the throne.
But he has also carved out a distinct and highly visible role for himself in public life by wading into topics that interest him.
Graham Smith, head of Republic, a campaign for an elected head of state, told The Guardian that the publication of the memos "will change the public perception of the monarchy as apolitical and harmless, to being a serious political force".