The King is “hugely frustrated” that his recovery from cancer is taking a “little longer” than expected, his nephew Peter Phillips has revealed.
Charles, 75, is “pushing” his staff to allow him to take on more royal duties and is determined to return to his normal work pattern as soon as possible.
Mr Phillips, the Princess Royal’s son, gave a rare insight into the King’s state of mind during an interview on Australian television.
“I think ultimately he’s hugely frustrated,” he said.
“He’s frustrated that he can’t get on and do everything that he wants to be able to do.
“But he is very pragmatic, he understands that there’s a period of time that he really needs to focus on himself.
“But at the same time he is always pushing his staff and everybody – his doctors and nurses – to be able to say ‘actually can I do this, can I do that?’”
Mr Phillips, 46, added: “I think the overriding message would be that he’s obviously very keen to get back to a form of normality and is probably frustrated that recovery is taking a little longer than probably he would want it to.”
The revelation chimes with observations made by several people who have worked alongside the King in recent weeks, who admit that in the absence of public duties, he is “keeping them on their toes” with floods of ideas and suggestions in even greater volume than normal.
Charles has been receiving treatment for an undisclosed form of cancer since early February.
The diagnosis was made following treatment for an enlarged prostate.
Just weeks later, it emerged that the Princess of Wales was also undergoing “preventative chemotherapy” after cancer was discovered following her abdominal surgery in January.
Mr Phillips told Sky News Australia that the Princess was “remarkable” and that she and Prince William had “got it right” in balancing their public life and family life.
He also spoke about how Princess Anne, 73, was not remotely bothered about media coverage, preferring to get on with the job.
He said: “I think in the past she has not always been the media’s favourite so to speak. But she’s never really let that bother her.
“She just keeps her head down the whole time and keeps working away and leaves others to worry about column inches.”
Paying tribute to his mother, who has long been dubbed the hardest-working royal, he said it was “pretty remarkable” that she was still carrying out overseas trips in her 70s.
Mr Phillips said the “work ethic” of both the Princess and his father, her first husband Capt Mark Phillips, had been hugely influential for him and his sister Zara Tindall.
“Both of them are incredibly hard-working and both in their 70s they’re still working a lot harder than either of them probably expected,” he said.
“But then as my mother always says – from that perspective, they had pretty good role models from my grandparents who were still working in their 90s.
“So everyone has a huge amount to live up to and ultimately they all live by example.”
He added that Anne “really valued” her home time to be able “to relax and just get to some form of normality”.
Mr Phillips is in Australia to represent the International Foundation for Arts and Culture.
He said the Royal family had a “huge affinity” with the country, adding: “All of us have friends over here.”