It is not a moment Malcolm Turnbull ever imagined in his younger years, but overnight the Prime Minister, an avowed republican, met Queen Elizabeth II.

Key points: "Most Australian republicans are Elizabethans as well," Malcolm Turnbull says

"Most Australian republicans are Elizabethans as well," Malcolm Turnbull says He believes another referendum would not be supported by the majority during the Queen's reign

He believes another referendum would not be supported by the majority during the Queen's reign Mr Turnbull paid tribute to the 91-year-old monarch's "selfless public service"

"Politics is full of unpredictable events," he said during a press conference before his visit to Buckingham Palace.

"All I can say is ... most Australian republicans are Elizabethans as well."

Mr Turnbull, who co-founded the Australian Republican Movement (ARM) and led it during the 1990s, believes another referendum would not be supported by the majority of Australians during the Queen's reign.

The ARM is currently pushing for an advisory ballot in 2020 to determine whether voters want an Australian head of state and how that person should be chosen.

That would then be followed by a referendum in 2022.

The Opposition had urged the Prime Minister to raise the issue with Her Majesty, but Mr Turnbull refused to reveal what he would say to the Queen because "discussions ... are always confidential".

He did, however, pay tribute to the 91-year-old monarch's "selfless public service" and described the meeting as "an honour".

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"I obviously look forward to her advice and wisdom," he said.

"She's after all known and advised many, many prime ministers."

Mr Turnbull also refused to say whether he would raise the release of the Palace Letters — the communication between former governor-general Sir John Kerr and the Queen ahead of the Whitlam government's sacking in 1975.

Historians say the letters are extraordinarily significant historical documents and will give new insight into the most dramatic event in Australian political history.

They have not been released by the National Archives because they are marked as personal papers, rather than official.

They are ordered to remain closed until 2027 and after that time the Queen could still veto the release.

Mr Turnbull's visit to Buckingham Palace was his last formal event on a week-long trip to Germany, France and England.