The man who would be king, eventually: Prince Charles turns 70

"He's complicated"

Charles' supporters say he is easy quarry, with every action and utterance scrutinised by an often unsympathetic media.

"When you're in his very exposed public position, loyalty and disloyalty is a quite complex situation," said a former senior aide who worked with the prince for many years.

He said detractors simply chose to view Charles's characteristics in a bad light.

"There's a whole load of stuff that is just not true," the former aide, who spoke on condition of anonymity, told Reuters. "Bower's only spoken to people with a grievance."

So what is he really like?

"He's complicated. I've rarely met anyone so curious about the world as him and eager to know what's going on and why. More than anything, he's got this drive, he's phenomenally hard-working," the ex-aide said.

Simon Lewis, the queen's communications secretary from 1998 to 2001, described Charles as full of enthusiasm, committed, with a "wicked sense of humour".

"If you are a public figure ... if you put your head above the parapet then you get criticism," Lewis told Reuters.

Friends and foes speak of his devotion to duty. The prince's working day starts at breakfast - he doesn't have lunch - and finishes near midnight, every day. The ex-aide said he got a work-related call from Charles on Christmas Day.

In private, Charles is passionate about arts, culture, theatre, literature, opera and pop - he's also a big fan of Leonard Cohen.

Happiest in his garden, he's loves Shakespeare, paints watercolours and has written children's books. He can be fun but also short-tempered and demanding, the former aide said.