Princess Diana's letters are exempt from Freedom of Information laws
Private letters between Princess Diana and the government are to be kept secret, the Information Commissioner has ruled.
A request for them to be made public was rejected on the basis that they were "of a personal nature".
The Royal family is exempt from the Freedom of Information Act, unless it is deemed to be in the public interest.
The princess died in 1997 when the car in which she was travelling crashed in a Paris tunnel.
Dodi Al Fayed and chauffeur Henri Paul also died when their Mercedes crashed in the Pont d'Alma tunnel.
The Information Commissioner's Office (ICO) said that the Diana letters were unrelated to government business.
Deputy Information Commissioner Graham Smith said: "It is important to draw a clear distinction between matters of public interest and matters about which the public may be merely curious."
This request was first made in October 2006.
The letters were withheld by the Cabinet Office then, at a time when it released birthday telegrams from the princess to various prime ministers of the time.
A further review by the Cabinet Office upheld this decision to keep the correspondence secret, stating that the public interest in not releasing it "outweighed" any gained by making it freely available.
This latest ruling by the ICO, the appeal board for any Freedom of Information requests, has upheld these previous decisions.