Princess Anne is a staunch ally of the King, but it seems they may not see eye to eye on plans to modernise the Royal Family.
Charles, 74, has long been in favour of updating the institution by trimming it, and he has already laid the groundwork for the task.
But in her most candid interview ever, Anne has said a slimmed-down monarchy “is not a good idea”.
A royal insider said: “While her overall tone was incredibly positive and honest, there are some raised eyebrows over the logic of entering the ‘slimmed-down’ argument.
“It certainly goes against the message from the top.
“The King and Prince of Wales are aligned that the institution needs to be more self-aware now than ever in its history, and such comments could be considered as an act of self-harm.”
Anne also talked about her brother’s suitability for the role of King and her sadness at losing their mother, while also mounting a passionate defence of the Royal Family.
The late Queen’s only daughter, often labelled the “hardest-working member of The Firm”, insisted the institution brings “long-term stability”, “continuity” and “goodness” to the UK and Commonwealth.
Anne also revealed moving details of how Covid “robbed” the late Queen and Prince Philip of vital interaction and stimulation in their final years. As calls grow for modernising the Royal Family and ensuring it gives value for money, Palace sources say the King is “acutely aware” of the financial pressures on people during the cost of living crisis.
A Mirror poll last week revealed 80% of Brits agree with him about a slimmed-down monarchy.
But speaking to Canadian public broadcaster CBC, Anne made her objections clear.
When the idea of a slimmed-down monarchy was raised by the interviewer, the Princess Royal gave a nod to the shock exits from the royal fold of the Duke and Duchess of Sussex and disgraced Prince Andrew.
Anne said: “Well, I think the ‘slimmed down’ [monarchy] was said in a day when there were a few more people around to make that seem like a justifiable comment.”
When it was put to her the world changes, Anne said: “It changes a bit.
“I mean, it doesn’t sound like a good idea from where I’m standing. I’m not quite sure what else we can do.”
Anne, who has been referred to as the King’s “trusted lieutenant” and who will play a starring role in the Coronation on Saturday, spoke to CBC hours before a poll in Canada found 54% there want to break ties with the monarchy.
Amid a wave of republicanism, especially in the Caribbean, Anne was asked if there are “conversations about relevance” for the Royal Family.
She said: “There will be, everywhere. It’s not a conversation that I would necessarily have. I think it’s perfectly true it is a moment where you need to have that discussion.
“But I would underline that the monarchy provides... a degree of long-term stability that is quite hard to come by any other way.”
She added: “Well, we don’t in many respects need to deal with it.
“We as a family see ourselves there to support that role.
“What we do, we hope, contributes to the monarchy and the way in which it can convey continuity, of not just interest, but of service, of understanding, the way that people in communities want to live their lives.”
Anne also told of her regrets at seeing her parents’ final years being affected by the pandemic.
She said: “Covid stole from my father, who lost a lot of the people who would have gone to see him and talk to him and have those conversations that would have kept him interested. He lost all of that.
“I’m sure that there are lots of families who will tell you the same thing. For the older generation, losing those contacts... online didn’t do that for everybody.” Clearly moved, Anne also reflected on her sadness about her mother’s death last year.
And on the image of her mother mourning alone at Prince Philip’s funeral in 2021 during Covid restrictions, Anne was asked if this was a “thievery”, she said: “Yes, you’re right.
“In some ways I’m glad we didn’t see that, at that moment.
“When you see the photograph it’s much worse somehow.”
Touching on the nation’s mourning following Her Majesty’s passing, Anne said: “I think we took a lot of it in, partly because we knew the route and I did actually spot people I knew on the way.
“It was such an impressive sight and it was... really touching in the way that people responded.
“People brought their ponies and horses out... They plaited them, they were properly dressed and well-turned out.
“They brought their tractors out, and parked them tidily, they were all clean. If you come from a rural background I was really impressed. It was just an astonishing sight.
“But the sheer numbers of people who turned up in quite extraordinary places. You’re never going to miss that and the atmosphere it created.”
In a lighter moment, the 72-year-old who is renowned for her no-nonsense style and her sense of humour, joked how Charles is exceptionally well-prepared to be King after being the longest heir in history.
Anne said: “Well, you know what you’re getting, because he’s been practising for a bit.” She added: “And I don’t think he’ll change.
“He is committed to his own level of service. That will remain true.”
She also revealed how the King will continue to address Britain’s role in the transatlantic slave trade.
As Buckingham Palace assists with landmark research into the monarchy’s involvement in slavery, Anne said: “Slavery hasn’t gone away.”
With the royals costing the British taxpayer £100million last year, aides have suggested cost-saving measures continue to be examined. A royal source said: “The King is very aware of giving value for money, especially in such testing times.
“But the design of a slimmed-down monarchy was in the planning before the notable exits of senior members of the family in recent years.”
In the Mirror poll, more than half said they think Charles should foot the £250m bill for the Coronation.
