The trio of commoners who all married into the top tier of British aristocracy – Queen Camilla, Catherine, Princess of Wales and Sophie, Duchess of Edinburgh – along with Anne, Princess Royal, are in the King’s inner circle.

And, as head of state, he will rely heavily on them as he seeks to tread the difficult path of modernising the monarchy and furthering his own interests – such as the environment – while supposedly not interfering in politics.

Other tricky issues include recriminations over the monarchy’s historical connections to slavery, allegations of unconscious bias within the ranks and the possible rise of the republic movement both in Australia and elsewhere.

He also needs to deal with the family rogues, including his rebellious son Prince Harry and wife Meghan Markle, as well as his scandal-hit brother Prince Andrew, who is threatening to write his own tell-all memoir.

“In my opinion Charles knows who he likes and who likes him,” royal expert Robert Jobson, who has just published a biography of the King, said.

“He wants to be a leader, rather than be led.

“He will do as much as he can to make his reign a success, but has limited time.

“He has to deal with a lot of difficult issues.

“The women in his life are crucial because they bring balance and calmness.”

Charles’ number one ‘go to’ for advice is his “darling wife” Queen Camilla, 75, who isn’t just there to jolly him along when his feathers are ruffled or when his pen leaks, she’s also his fiercest protector and a huge influence on him.

By managing to go from public enemy number one to Queen, not just Queen Consort, she’s proven to be a savvy courtier, who understands how to deal with the men in grey suits in fusty palace corridors who keep The Crown ticking over.

She also knows when the big calls need to be made.

When Charles’ loyal aide and head of his charity, Michael Fawcett, was caught up in the cash-for-honours scandal, Camilla made it clear she wanted him gone, despite his 40 years of service.

He was later cleared of any financial impropriety, but nevertheless she feared he was harming Charles’ future.

Royal commentator Katie Nicholl said Camilla “was never really a fan of Fawcett, and she could see how damaging this could be to Charles’ reign”.

“She is there to look over him,” Jobson added, author of King Charles III, Our King: The Man and the Monarch.

“Camilla is his number one gatekeeper.

“She will make sure that those she believes are not acting in his best interests are kept away.”

Catherine, the Princess of Wales, 41, is the devoted daughter-in-law, and has a vested interest in the future of the monarchy, with her husband Prince William, the king-in-waiting and son George a future monarch himself.

Photographs of the pair together appear to show a genuine bond between Charles and Kate.

“She’s a great mum and a great wife,” Jobson said. “She has not put a foot wrong. What father-in-law would not love her?”

He said her role is to keep the nuclear family tight and ensure the next generation of royals emerge as stable adults, prepared for a life in the public eye.

Perhaps her greatest asset for Charles is that she has the common touch. Her upbringing was decidedly middle class.

She’s also “the star of the show”, Jobson said, and the monarchy needs a bit of glamour to keep it on the front pages.

Charles’ sister-in-law, Sophie, Duchess of Edinburgh, 58, was running her own PR firm when she met the King’s youngest sibling Edward, so knows a bit about “optics”.

She was a favourite of the Queen, with which she had a close and loving bond.

She is also the patron of more than 70 charities and organisations and is not afraid of stepping up and flying the flag for the UK.

While she has not received the same level of media attention as other royals, she is becoming more visible, and her new title, Duchess of Edinburgh, reflects the importance of her role within the royal circle.

“Sophie’s a real asset,” Jobson said.

“Charles knows he can trust her and she’s a safe pair of hands.”

The fourth member of the female quad is Charles’ sister, Anne, who is often referred to as the hardest working royal.

She has been a loyal servant to her mother and the monarchy her whole life.

And, there doesn’t appear to be any resentment on her part that she is the ‘spare’, unlike Prince Harry.

She chose not to pursue the option of giving her children royal titles, telling Vanity Fair in 2020, “I think most people would argue that there are downsides to having titles … So I think that was probably the right thing to do.”

Known for her no-fuss attitude, Charles will always get a brutally honest answer from Anne.

He also loves Anne’s daughter Zara who is a “riot”, according to Jobson. “His eyes light up when he sees her”. She would also be someone he could ask an opinion and know it was safe to do so.

However, his other nieces, Beatrice and Eugenie, who reportedly have asked to have private meetings with the King about their father Prince Andrew’s future, are too influenced by him and their mother.

Andrew’s ex, Sarah Ferguson, who remained close to the Queen, is not invited to the Coronation and has made too many poor decisions herself to ever be someone Charles would seek serious advice from.

And, what might have been … Meghan, an American “woman of colour”? She would have been an international asset for Charles and the monarchy.

But once she realised she couldn’t dictate to them how to run the ship, she tried to blow it up.

Whether Charles and Meghan ever manage to patch up relations, so they can be on friendly terms remain to be seen. But for the sake of the monarchy, she’s too dangerous to ever be allowed back into Charles’ inner circle.