The King’s nephew Peter Phillips has said Charles is “frustrated” that his recovery is taking longer than “he would want it to”.
The son of the Princess Royal said the King was “in good spirits”, but was “pushing” his staff to be able to return to his duties after beginning treatment for cancer last month.
In a televised interview, Mr Phillips told Sky News Australia: “I think ultimately he’s hugely frustrated.
He's frustrated that he can't get on and do everything that he wants to be able to do
“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?'”
Charles has been receiving treatment for an undisclosed form of cancer since early February after he was treated for an enlarged prostate and on Friday the Princess of Wales revealed she was undergoing preventative chemotherapy for cancer.
Mr Phillips 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 son of Anne, 73, and her first husband Captain Mark Phillips, said during the interview on Australian television that his mother “leaves others to worry about column inches”.
Mr Phillips 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.”
The eldest grandchild of Queen Elizabeth II added that it was “pretty remarkable” that his mother was still carrying out overseas trips in her 70s.
Mr Phillips said the “work ethic” of his parents had been hugely influential for him and his sister Zara Tindall.
He added: “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.
“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 was on a visit to Australia to represent the International Foundation for Arts and Culture.
He said the royal family had a “huge affinity” with Australia, adding “all of us have friends over here”.
