The Queen was not informed in advance about the 1975 dismissal of Australian Prime Minister Gough Whitlam, newly released letters show.
Mr Whitlam’s government was removed by her representative at the time, Governor-General Sir John Kerr, and replaced with an opposition party.
It is considered the most controversial event in Australian political history.
The letters, released after a court battle, show Sir John wrote it was “better for Her Majesty not to know”.
However, in earlier letters he had discussed with Buckingham Palace whether he had the constitutional powers to be able to dismiss the prime minister.
Historians have long questioned what the palace knew about the removal of Mr Whitlam, a progressive whose reforms divided Australia after two decades of conservative rule.
More than 200 letters have been kept sealed in the National Archives since 1978, but were released on Tuesday for the first time.
In May, the High Court of Australia ruled they could be accessed in the national interest following a challenge by historian Prof Jenny Hocking.
What happened to Gough Whitlam?
Mr Whitlam and his Labor Party came to power in 1972, implementing policies which many celebrated, but he grew less popular amid a troubled economy and a fierce political opposition.
On 11 November 1975, he was sacked on the justification that he had failed to get parliament to approve a national budget and then subsequently declined to resign or call an election.
As Australia is a constitutional monarchy with the Queen as head of state, the governor-general claimed he had the authority to do this.
However this “reserve power” to remove an elected prime minister who held a majority in the House of Representatives has been debated ever since by legal experts.
His dismissal was an unprecedented action which shocked the country and prompted questions about Australia’s political independence from Britain.
Some viewed it as a “constitutional coup” and an overreach of the “royal prerogative” , sparking strikes and violent demonstrations as well as discussion about the country becoming a republic.
But others celebrated his departure. In a general election held just over one month later, voters overwhelmingly elected Malcolm Fraser’s centre-right Liberal Party – which had been acting as a caretaker government.