PM's reminder: Charles will be our king

Malcolm Turnbull has reminded Australians Prince Charles will become their king if the constitution isn't changed.

The prime minister is scheduled to have an audience with the Prince of Wales later on Wednesday in Canberra.

"If Charles becomes the King of the United Kingdom - and I've got no doubt he will be - unless our constitution has been changed, he will become the King of Australia," Mr Turnbull told reporters.

Asked by veteran journalist Laurie Oakes if he was happy about that prospect, the avowed republican said: "I'm a happy person. There's never been a better time to be an Australian."

Fortunately for Mr Turnbull a closing lift door prevented him from saying whether he would be mentioning the republic to the prince during their meeting.

A new poll shows only 27 per cent support for Prince Charles becoming King of Australia.

Essential Research polling , commissioned by the Australian Republican Movement, also showed that 51 per cent of voters support replacing the monarch with an Australian citizen.