King Charles' cancer diagnosis is casting doubt on his future role.

The Palace reports he will continue official duties until further notice.

Sydney University Constitutional Law expert Anne Twomey says what duties he performs, remain within his control at this stage.

But she says if he becomes incapacitated, decisions will move to his spouse Queen Camilla, two Parliamentary officials and two people from the court.

"Amidst those five, if three of them decide that he's incapable of fulfilling his activities, he can have a regent. And then the regent can take over his powers."

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