The transformation of Queen Camilla from understudy to centre-stage star will, no doubt, continue to be discussed by historians many decades from now.

When she married the King almost 19 years ago, royal aides were at pains to stress that the then Duchess of Cornwall very much saw herself as an adjunct.

Her role, they said, was to support her husband in the pursuit of his increasingly heavy royal duties, while building up a small portfolio of patronages she was keen to support.

No one in her orbit – let alone the lady herself – dreamed that she would one day be crowned at her husband’s side (with the blessing and approval of Queen Elizabeth, no less), let alone stand in for His Majesty at events such as today’s annual royal Maundy service in Worcester.

It is the first time a consort has ever performed this duty on behalf of a monarch in British history.

While King Charles diligently continues to undertake daily state business behind the scenes despite his ongoing cancer treatment, Queen Camilla now finds herself, to all intents and purposes, his front of house.

Queen Camilla departs the royal Maundy service at Worcester Cathedral today

Once considered to be one of the most hated women in Britain, many have been won over by her warmth, humour, strong sense of duty and, frankly, classic British ‘let’s just keep this bloody show on the road-ism’.

Speaking to me on Tuesday at a Clarence House reception to mark three years of Camilla’s phenomenally successful book club, The Queen’s Reading Room, national treasure Dame Joanna Lumley was one of many queuing up to sing Her Majesty’s praises.

‘They [the Royal Family] are all extremely dutiful. It’s like the theatre – if someone is ill, someone steps into their place, the understudy keeps the show going,’ she said.

‘She is the epitome of professionalism and public service.

‘Everyone thinks she should be blubbing in a corner, but this is not what these people are made of. And it’s something we should aspire to.

‘If you sit alone feeling sorry for yourself you will feel sad and tragic. But if you get up and do something with a smile, then you feel better. ‘

Best-selling thriller writer, Harlan Coben, agreed. ‘She’s a keeper, as we say in America,’ he enthused.

One royal retainer, who has witnessed many of the family’s twists and turns over the years, told me recently that they are genuinely glad to see Camilla’s diligence and sense of duty recognised at long last.

‘She’s been an absolute trooper, really she has,’ they said. ‘She’s worried about her husband, everyone is. His Majesty is doing amazingly well but it’s tough to see someone you love go through an experience like this.

‘And yet she just gets up and goes out there, doing exactly what’s asked of her with a smile on her face.

Queen Camilla poses with the Maundy Party during the royal Maundy service

‘I always think you see the best of people at the worst of times, and I really hope people realise how true that is here.’

Like many people caring for a loved one with a serious illness, Camilla is torn between being by her husband’s side and doing what’s expected of her.

But she knows the King (she respectfully never publicly refers to him as anything but the King or His Majesty, even to those she knows well) hates being fussed over and still has a prodigious work ethic.

‘She’s spending as much of her time as she can with her husband but also believes that one of the best ways she can support him is by going out in public to represent him,’ one aide remarks.

Another member of their circle says: ‘She’s absolutely out there leading from the front.’

Of course, Buckingham Palace isn’t blinkered. Senior courtiers know full well that there will always be a vocal – and not necessarily small – group of people who will never accept Camilla on the throne (despite more than 2,000 genuinely excited people coming out to see her in Shrewsbury on a very wet, working Wednesday this week).

But they also believe there is no point in wasting energy trying to convert the naysayers, and should let the Queen’s actions speak louder than their outdated murmurs of disapproval.

Indeed, at Clarence House this week you simply wouldn’t have known that anything was wrong, apart from the odd whispered words of condolence.

Queen Camilla arrives at the royal Maundy service, deputising for King Charles during his cancer battle

She greeted dozens of guests from the literary and acting worlds, gave a short but well-received speech about the benefits of reading and even gamely looked down a microscope at a brain cell for the benefit of the cameras.

All, let us not forget, while His Majesty was literally above our heads, upstairs, recuperating from his latest bout of cancer treatment and working.

Whatever you might think of her, that takes gumption.

That’s something King Charles genuinely adores about his wife, with whom he will celebrate almost two decades of marriage on April 9. She’s stood by his side through thick and thin, loves him for who he is and just gets on with things.

Friends say she’s one of life’s ‘onwards and upwards’ characters and still makes the King laugh more than anyone in the world. In fact, she was considered something of a ‘tonic’ at his hospital bedside in January.

‘Honestly, she’s hilarious,’ a friend says. ‘Really lightens the atmosphere. She doesn’t bring flowers but does come with a lot of laughter, which is often what His Majesty needs.’

Today Their Majesties will transfer to Windsor Castle, a place which has grown increasingly dear to their hearts.

Springtime at Windsor is one of the most glorious seasons of the year: daffodils carpet the grass and primroses peek from underneath the blooming cherry trees.

It will provide a brief moment of private respite, apart from their very public visit to St George’s Chapel on Easter Sunday, which the King is determined to lead (on foot and in front of the cameras, I’m told).

By his side, smiling as always, will be his Queen.

No longer the understudy, but very much a leading lady in her own right.