TalkTV Royal Editor Sarah Hewson says it’s her understanding that King Charles and Queen Camilla knew about the King's cancer diagnosis last week.

“Queen Camilla opened a Maggie's cancer care centre – I’m told that she did that knowing the diagnosis,” Ms Hewson told Sky News Australia host Piers Morgan.

“We think that she knew by that point.

“My understanding is that she carried on with that engagement and it will have taken on an added significance of course, for her.

“We know that the King told his siblings, Anne, Edward and Andrew …before this was made public.”