Queen Elizabeth II was not warned of the Australian Prime Minister's dismissal by her representative in the country in 1975. The letters were kept secret for decades and published on Tuesday.
The representative of the British monarch in Australia, Governor General John Kerr, triggered a constitutional crisis when he released Gough Whitlam, the popular leader of the center-left Labor party, without warning.
In May, the High Court ruled that more than 200 letters between the Queen's private secretary and Kerr, including many dealing with the controversial matter, should be published.
Although the correspondence shows that the queen was not informed immediately before Whitlam's release, they confirm that Kerr had exchanged letters with the palace for months about his powers to overthrow the prime minister.
Suspicion that the palace played a direct role in Whitlam's fall was long held by Australian Republicans who argued that the country should break with the monarchy.
The Australian National Archives released the 1,200 pages known as "Palace Letters" on Tuesday after a four-year legal battle to keep them hidden, which is reported to have cost $ 2 million ($ 1.4 million).
Historians are now searching the documents to determine if the British government has attempted to influence events in their former colony and what role the Queen, Prince Charles and the best royal advisors may have played.
A key extract shows that Kerr informed the Queen that he fired Whitlam shortly after the November 11, 1975 intervention.
"I should say that I have decided to take the step that I have taken without informing the palace in advance because the Constitution places responsibility on me and I thought it was for your majesty it was better not to know in advance, although it is, of course, my duty to tell her immediately, "he wrote.
The decision ended a protracted political stalemate after the opposition-controlled Senate refused to approve the government's budget, significantly weakening Whitlam's position.
The letters confirm that the palace knew that Kerr had considered the options available to him under his constitutional "reserve powers", including the dismissal of the Australian leader, a measure no other governor-general has taken before or since.
Kerr appointed liberal opposition leader Malcolm Fraser interim prime minister, which caused chaos in Canberra and protested parliamentary action.
Fraser won a landslide election later that year.
Australia became independent in 1901, but the queen is still head of state. A referendum on the republic failed in 1999.
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