A legal battle has begun over secret letters revealing what the Queen knew of her Australian representative's plan to dismiss Australia's government in 1975.
The case could finally solve a mystery behind the country's most dramatic political crisis.
Historian Jenny Hocking is asking the Federal Court to force the National Archives of Australia to release the letters between the British monarch, who is also Australia's constitutional head of state, and her former Australian representative, Governor-General John Kerr.
The Archives have classified the letters as "personal", meaning they might never be made public.
The letters would reveal what, if anything, the Queen knew about Kerr's plan to dismiss prime minister Gough Whitlam's government in 1975 to resolve a deadlock in Parliament.
It is the only time in Australian history that a democratically elected federal government was dismissed on the British monarch's authority.
The dismissal stunned Australians and bolstered calls for the country to sever its colonial ties to Britain and become a republic.
Mr Whitlam's own son, lawyer Antony Whitlam, is arguing the case on behalf of Ms Hocking, and took on the case free of charge.
Ms Hocking, a Whitlam biographer, argues that Australians have a right to know the details of their history, and that the letters written in the months leading up to the unprecedented dismissal are key to unravelling the truth.
"It needs to be settled once and for all," she said during a court recess.
"There's a lot of uncertainty in this."
Antony Whitlam argued that the letters should be viewed as official, rather than personal, documents in part because the relationship between the governor-general and the Queen is an official one.
"It couldn't seriously be suggested that there was a personal relationship between the Queen and John Kerr," he told the court.
If the letters lose their "private" and "personal" classification, they are free to be made public 30 years after they were written like other government documents held in the Archives.
That means they could be available immediately.
Lawyer Tom Howe, who is representing the Archives, told the court that there was a distinction between the institution of the governor-general and the governor-general himself.
The governor-general himself, Mr Howe argued, is not a national institution, and thus his personal records are owned by him and are not subject to the Archives Act.
The Act allows for the release of official records.
Questions and conspiracy theories still swirl about the motivations surrounding the prime minister's dismissal.
Sir John, who died in 1991, said the decision to oust Mr Whitlam was his alone.
However, some Australians believe the Queen had a hand in the decision.
One of the most spectacular theories is that the US Central Intelligence Agency ordered Mr Whitlam's dismissal because the agency feared his government would close a top-secret US intelligence facility in the Australian Outback.
Sir John rejected that theory as false.
Before 1975, few Australians realised the governor-general - whose role is largely ceremonial - had the power to fire a prime minister during a constitutional crisis.
That crisis began when the opposition party tried to force Mr Whitlam to call general elections by blocking routine legislation in the Senate that allowed the government to pay public servant salaries and provide services.
Mr Whitlam refused to call an election, sparking a weeks-long constitutional impasse.
Sir John then fired Mr Whitlam, called an election and appointed opposition leader Malcolm Fraser as prime minister.
Weeks later, Mr Fraser's coalition won an overwhelming election victory.
Critics of Sir John dubbed his firing of Mr Whitlam an ambush, and said the governor-general should have warned the prime minister that it was coming.
Sir John said he was worried Mr Whitlam would have fired him first if he had tipped him off ahead of time.
Monday's hearing was the only one scheduled in the case.
Federal Court Justice John Griffiths is expected to issue a ruling at a later date.