What to expect if Charles becomes King
From the outside, Prince Charles' 70th birthday celebrations this week appeared jovial, an important milestone for the monarch-to-be, marked by lavish celebrity-packed parties.
But inside, royal observers say the occasion for Charles would have been somewhat poignant, as he prepares for a life even more busy than the one he knows and one of less charity work and opinion.
Indeed, just last week, in an intimate interview with the BBC, the Prince was asked whether his outspoken views would continue when his reign as King begins.
"No, it won't. I'm not that stupid," he replied.
MAKING OF A KING
He theoretically became heir apparent in 1952 when he was three years old (although a regent would have served if his mother had died before he attained adulthood), and has been in the shadow of Queen Elizabeth II his entire adult life.
Sixty-seven of his 70 years have been spent preparing for the role of King.
"He's reached the age where most people are thinking about retiring," royal biographer Penny Junor said.
"Some people at 70 are in old peoples' homes already and they're slowing down … He has not yet got the position that he's been trained for."
The Queen's relationship with her son has not been the closest, and Ms Junor said Charles would be touched by her having hosted a birthday party for him.
"He adores his mother but it's not close," she said of their relationship.
"I think that probably the problem was, when he was a child, she was juggling being Queen at a very young age with being a young mother as well.
"It was unthinkable at that time that she should take her children with her when she went on foreign tours."
While Charles reveres his mother, Ms Junor said there had never been a "huge amount" of warmth between the pair and that the Queen, 92, acknowledges there is very little he does not know.
"What would she say to him? He's 70 years old," the biographer said.
"There's not a lot that a mother can tell a 70-year-old.
"He's seen papers of state, he's met prime ministers.
"But he has been observing her.
"He will be the best prepared monarch that this country has ever had."
Editor-in-Chief of Majesty Magazine and royal author Ingrid Seward said Charles has known he was destined for the crown his whole life.
"That's what he's been groomed to be, it's just that it's come very late," she said.
"He's said in the past he doesn't particularly want to think about it - when his mother is no longer there."
CHARITY WORK AND BECOMING APOLITICAL
Once the Prince becomes King, he won't have as much time to devote to his beloved charities.
For 40 years, Charles has supported many philanthropic causes including his own charities The Prince's Trust Group and The Prince of Wales Charitable Fund.
He has genuinely enjoyed his charitable works, but in 1987 he did say he always felt as though he was in a rush.
"The trouble is I always feel that unless I rush about doing things and trying to help furiously I will not (and the monarchy will not) be seen to be relevant and I will be considered a mere playboy," he wrote in a private letter.
He's also gained a reputation for being politically outspoken on issues such as climate change, environmental conservation and Islam.
It's these contentious opinions that royal commentator Claudia Joseph believes Charles will have to suppress when he becomes King.
"He is known for writing lots of letters to government ministers and lobbying them about his pet interests, such as the environment, but he will be expected to be apolitical when he is monarch," she said.
"He will have to steer a more cautious path."
Ms Seward said the Prince was "very much before his time".
"I remember years ago (Princess) Diana telling me Charles wouldn't let her use hairspray anymore because of the ozone layer," she said.
"People say he has old-fashioned views but I think he's very forward thinking."
Despite his array of charitable achievements - which his sons Prince William and Prince Harry are now also rigorously pursuing - the Queen has rarely praised her son in public.
Ms Junor said the Prince had never felt that he was good enough for his mother or father, Prince Philip.
"That's part of Charles' problem in life, he doesn't have huge self-confidence," she said.
"I think he has more confidence now since Camilla (his second wife).
"I think she has been the making of the man.
"She will be the strength behind the throne."
THE DUCHESS OF CORNWALL
Despite the couple having been married for 13 years, an "anti-Camilla" sentiment is still palpable in Britain because of the country's great love for Charles' first wife Princess Diana.
"There is still a feeling that they (Britain) don't want Camilla to be Queen," Ms Seward said.
"When it actually happens people will just accept it totally."
The couple live at Clarence House in London and attend both domestic and international royal engagements, such as a recent visit to Ghana and Nigeria on a royal tour.
Royal author Robert Jobson has written in his new book, Charles At Seventy: Thoughts, Hopes and Dreams, that Camilla will become Queen once her husband ascends the throne, despite Clarence House issuing a statement when the couple married that she would instead be known as consort.
That statement was quietly removed from the royal family website earlier this year.
Charles was also endorsed by the leaders of the Commonwealth nations at the CHOGM event in London earlier this year to be the new head of the Commonwealth when he eventually takes over from his mother as monarch.
A KING OF CHANGE
While the new monarchy will not bring immediate changes, Ms Junor said changes would come under a King Charles.
"If Charles did everything that the Queen has done, that would be quite wrong," she said.
"I think William (Charles' oldest son) in his turn will bring something completely new again.
"Not radically new but they learn from one another and they understand what works."
Ms Seward agrees change is inevitable.
"I know he (Charles) wants a slimmed down monarchy," she said.
"It will be concentrated on to his sons I think and their family.''
She doubted Charles would be as popular as Queen Elizabeth, who vowed as a 21-year-old princess to serve her people until she died, effectively ruling out abdicating in favour of her son.
"I don't think anyone will be as loved as the Queen,'' Ms Seward said.
"A lot of people have never known anything else.
"I think he (Charles) will make a very good king, when it comes, if it comes."