It is understood that a "functionary" working for the Prince gave details to Stuart Higgins, the editor of the Sun newspaper which broke the story.
Mr Higgins refused to disclose his source for the world exclusive saying: "There's no point in you asking. I won't tell."
But Buckingham Palace's swift confirmation on Wednesday night of virtually every point revealed from the explosive correspondence appeared to confirm suspicions that the leak was carefully calculated. "It came from Charles's side via a functionary who has no particular allegiances to either party. One has to assume it was with Charles's permission," one source said.
At the House of Commons, the story was widely believed to have come from Whitehall.
That the details were given to the Sun was particularly interesting given Mr Higgins's very vocal support for the Princess after her Panorama interview.
Although both the Prince and Princess have used the media in their feuding, she had little to gain from this disclosure as it appears to be precipitating the divorce she has opposed.
However, the Prince's camp was keen to distance itself from the leak. One insider said: "The Sun were attributing it to political sources. I really don't know how it emerged. One would like to think that the substance of the Queen's letters to her family might remain private."Reuse content