With Princess Anne on his side, King Charles III's reign stands a ...

Princess Anne passed me last night on Albemarle Street, Mayfair, on her way to an Oswald’s dinner attended by several members of the British Royal Family, as well as their counterparts from Greece, Sweden, Monaco and Denmark. A hubbub ensued as she strode ahead of her husband, Vice Admiral Sir Timothy Laurence, wearing a functional puffer jacket, and pronging her umbrella into the ground with every swift step. This simple scene spoke volumes: Anne is a woman who walks and acts with purpose.

Princess Anne, Princess Royal during the Trooping the Colour parade

While today is King Charles III’s, it will also be one of Anne's finest moments.

Reportedly in ode to her ‘loyalty and unwavering devotion’ to the King, Anne will perform a starring role. As the newly crowned King and Queen leave Westminster Abbey in the Gold State Carriage, they will be followed by the Princess Royal, 72, on horseback, performing the prestigious ceremonial role of Gold-Stick-in-Waiting. She will lead 6,000 members of the armed forces from the Abbey, down the Mall to Buckingham Palace. It will be the largest procession since the coronation of Queen Elizabeth II.

The position originates from the 15th century, and is usually held by the Colonels of the Life Guards and the Blues and Royals. The office of Gold Stick is jointly held by the Colonels of the Life Guards and the Blues and Royals – a position Princess Anne has held since 1998. This role might be ceremonial, but it feels personal: Gold-Stick-In-Waiting is responsible for the monarch’s safety. It is no surprise that it is Anne Charles has chosen as his protector.

Princess Anne in the grounds of Sandringham, before the 1969 Royal Tour of Australia and New Zealand

‘She is the person The King has known longest,’ royal correspondent Wesley Kerr OBE tells Tatler. ‘She can be relied on for complete discretion and unconditional love. Anne is wise, intelligent, incredibly plugged into the modern United Kingdom. She understands completely who and what has shaped him and is eager for him to succeed: for the sake of their beloved mum and dad and for country and Commonwealth.'

Indeed, as Anne leads the procession, royal watchers might recognise this as a poignant moment that stirs memories of our late Queen Elizabeth II. Anne has previously performed the role of co-Gold-Stick-in-Waiting for her mother, together with Field Marshal Lord Guthrie of Craigiebank. ‘She will be extremely good as Gold-Stick-In-Waiting because she will be extremely helpful to the Household Cavalry and gives good advice, which they can benefit from,’ Lord Guthrie tells Tatler the day before the coronation.

Queen Elizabeth II and Princess Anne attend a function at the Hotel Imperial in Vienna

This visual will be significant: for Anne is the great protector; the bodyguard; the assurance. And it is with her undying, pragmatic support that King Charles III's reign stands a fighting chance. Anne's ‘just get on with it’ attitude cut through apathy and protests. When she's not supporting one of her 300 patronages, she's a countrywoman, a former Olympian, a sports fan.

And her friends agree. ‘I had a lot to do with her and like her very much,’ Lord Guthrie continues. ‘I admire her views and think she is very forward-looking. She is a great ally to King Charles and supporter of the constitution. She is very direct when she has a point to make - and that is good.’

‘The Princess Royal is one of the hardest working people I have ever met,’ Lord Coe, a close friend, told me last year. ‘She has exactly what her mother, Her Majesty The Queen had – which is that she is imbued with an extraordinary sense of public duty and service. She is down to earth but without a trace of maudlin sentimentality.’

King Charles III and Princess Anne, Princess Royal arrive for the state funeral and burial of Queen Elizabeth II

I find it interesting that an article of mine keeps coming up at social events. A tap on the shoulder and a whisper: ‘I loved your piece on the Princess Royal. She is just fantastic.’ They’re referring to an article I wrote in January: What Harry could learn from his aunt, Princess Anne. I have written about the Princess Royal before, and here I go again.

Because while Princess Anne has been called upon with increasing reliance for every major royal occasion – riding at Trooping the Colour to mark her mother's Platinum Jubilee, or guarding her mother's body on the three-day journey from Balmoral to Westminster Abbey – others have been sidelined. The is the only sibling to perform a ceremonial role. And she has risen above Charles's Duke dilemma. The traditional homage by royal dukes — which would have included Harry, Duke of Sussex, and Andrew, Duke of York — has been scrapped. And it's not difficult to work out why.

Princess Anne, Princess Royal and Vice Admiral Timothy Laurence are greeted by Station Commander Group Captain McPhaden at Northalt

Andrew and Harry are expected to be tucked away; to be transported back to the palace discreetly by car; perhaps not even to appear on the balcony for the flypast. Anne has an entirely different problem on her hands: she's got to dismount and get up to the balcony in time for the flypast, because she is an integral part of the star exhibit. Perhaps behind those doors, she'll have some sound words of advice.

Really, Anne might be King Charles III most important ally. In the same way that Queen Elizabeth II triumphed both as an individual and as part of the firm – we have all heard the phrase ‘I don’t support the monarchy but I do love the Queen’ – Anne is a great unifier. Lu Guthrie, Hon Secretary of Chelsea and Westminster branch of Save the Children, sums it up: ‘I have had ‘tea’ with her a few times, and I was amazed at how long she spent meeting everyone for four hours – and then on she went to another black tie event! A hard worker, which we all know.’

This princess is a trooper, and she’ll damn well get the job done: who can’t relate to that?