The Prince of Wales has pledged he will not be an interfering king and will reign as monarch in a similar way to his mother.
In a ground-breaking interview about his future role, the Heir to the Throne dismissed accusations that he does too much "meddling".
Prince Charles turns 70 next week and is the longest serving Prince of Wales in British history.
Asked if he planned to reign as king in the same interventionist way as he currently operates, he replied: "I’m not that stupid. I do realise that it is a separate exercise being sovereign.
"So, of course, I understand entirely how that should operate.
"The idea somehow that I’m going to go on in exactly the same way, if I have to succeed, is complete nonsense", he said. "Because the two situations are completely different".
The Prince told the documentary filmmaker John Bridcut: "You can’t be the same as sovereign if you’re the Prince of Wales or the Heir, it’s a different function."
The film, to be shown on the BBC on Thursday night, includes interviews with his sons, Princes William and Harry.
William says that he would "like to see his [father’s] passions and his interests and the things he’s been campaigning for, come to fruition for him".
While Prince Harry urges his father to "remain optimistic" and hopes he will be able to carry on his leadership role by getting "energy" from "his children and grandchildren and hopefully more grandchildren to come".
Prince Charles has been Heir to the Throne since his mother became Queen in 1952.
At the time, Charles was just three-years-old.
He was officially made Prince of Wales in an investiture in Caernarfon in 1969.
Because of his campaigning style, his speeches on climate change and architecture, and his interventions to help the disadvantaged, the Prince has often been accused of "meddling".
Charles says: "If it’s meddling to worry about the inner-cities as I did 40 years ago and what was happening there… the conditions in which people were living.
"If that’s meddling, I’m very proud of it."
"If you became sovereign", he adds referring to Shakespeare, "you play the role in the way that it is expected".
"You operate within the constitutional parameters."
- Camilla speaks about Charles’ destiny
In the programme, Prince Harry also spoke of the moment at his wedding when Prince Charles stepped in to walk Meghan down the aisle of St George's Chapel in Windsor.
"I asked him to and I think he knew it was coming and he immediately said: 'Yes of course, I’ll do whatever Meghan needs and I’m here to support you.'"
The Duchess of Cornwall also spoke about the moment her husband handed Meghan’s hand to Harry’s at the Royal Wedding and Harry said: "Thank you, Pa."
Camilla said: "I think that was very touching.
"Sitting where I was, you couldn’t hear what he said, but afterwards, watching it on the television, I think it was a lovely gesture."
Prince Charles and Camilla have just spent the last week on tour in West Africa visiting Ghana, The Gambia and Nigeria.
They will return home at the end of the week so that Prince Charles can, for the second year running, stand in for The Queen and lead the nation in mourning at the Cenotaph on Remembrance Sunday.
It’s another sign of the transition of duties from the Queen, now 92, to her son.
William and Harry also spoke about their own commitment to the environmental causes that they’ve had drummed into them from a young age – and their father seemed to appreciate that.
Charles said: “Your children always surprise you because you think they pull your leg all the time and appear not to pay attention at all.
"In fact, you later discover, perhaps they did."
Harry revealed, it’s because of his father that he still turns out the lights in the house, much to his wife Meghan’s surprise: “Why turn the lights off, you know it’s dark’’, Harry says, quoting the Duchess of Sussex.
The Duke says he answers: “We only need one light, we don’t need like six!”
The Prince will celebrate his 70th birthday on November 14.
- Prince, Son and Heir: Charles at 70 will air on BBC1 at 9pm on Thursday