The secrets of Gough Whitlam's dismissal will remain under wraps after a historian was denied access to letters between the Queen and then governor-general, who played such a crucial role in the prime minister's 1975 demise.
It is now down to the current prime minister to urge the monarch to lift her embargo.
Jenny Hocking went to the Federal Court seeking to have the National Archives of Australia release the so-called "palace letters".
She previously said the dozens of secret letters between Buckingham Palace and then governor-general Sir John Kerr in the months before the 1975 dismissal would give an insight into his thinking and how much the palace knew.
But the archives refused to release the letters because they've been deemed personal communications rather than official commonwealth records.
The court on Friday agreed with the archives. It ruled the letters were the personal property of Sir John and not the property of the Commonwealth.
Professor Hocking is disappointed "the secrets of the dismissal will remain".
Justice John Griffiths in his judgment acknowledged there was clear public interest in the records "which relate to one of the most controversial and tumultuous events in the modern history of the nation".
But he found no error in the decision of the National Archives of Australia, meaning the documents will remain sealed until at least 2027 when the existing embargo ends.
But even then the Queen holds a final veto over their release.
Prof Hocking said the "clear public interest" identified by the judge should compel Prime Minister Malcolm Turnbull to lobby the Queen for an early end to the embargo.
"Without such advice from the prime minister, critical aspects of our history - critical documents in our history that would enable all Australians to know and understand the full story of the dismissal of the Whitlam government - will remain secret," she said.
