SARAH VINE: As personally frustrating as the last months have been for Charles, there is one huge positive - how Camilla has shown herself worthy of not just being his Queen, but our Queen too

As Charles III prepares to celebrate the anniversary of his Coronation on May 6, he may well reflect on what has been a bittersweet first year as King.

Having prepared all his life for the solemn responsibility of succeeding his formidable mother to the throne, it must have been galling – to say the least – to find himself off games with a diagnosis of cancer.

At precisely the moment when he should have been hitting his stride, he was forced to slam the brakes on. Not easy for a man who has always been in something of a hurry to get things done.

Having prepared all his life for the solemn responsibility of succeeding his formidable mother to the throne, it must have been galling for the King to find himself off games with a diagnosis of cancer, writes Sarah Vine

Mail columnist Sarah Vine writes that when she first met Queen Camilla she was instantly made at ease by the then Duchess of Cornwall's manner

But every cloud has a silver lining. As personally frustrating as the past few months may have been, there has been one hugely positive outcome from his illness. And that is how Queen Camilla has shown herself to be worthy, not just of being his Queen (as she has undoubtably always been), but our Queen too.

I first met the Duchess of Cornwall, as she then was, many years ago at a dinner organised by mutual friends. She and the King were not long married, and she still hadn’t quite settled into the role as royal consort. He, as you might expect, had an air of old-fashioned formality about him, and was rather stiff and anxious. She was the opposite: warm, mischievous, conspiratorial, occasionally indiscreet. She instantly made one feel at ease – and by extension made him seem more relaxed, since it was abundantly clear that everything about her delighted him. If you made her laugh, he would chuckle too – that sort of thing. It was as though she were balm for his soul.

A long time after that, I was privileged again to dine privately with them, this time at Clarence House. The intervening years had changed us all greatly, but the Queen remained the same: warm, welcoming, gossipy, always that naughty twinkle in the eye. As for the King, he seemed so much happier, so much more comfortable in his own skin. I recall a happy, informal supper with delicious food and easy conversation. In many ways, theirs is one of the great love stories of our time, not least because they have overcome so many obstacles to be together.

But in people’s minds, the spectre of Princess Diana still looms large over their union. And it is understandable that Diana’s loyal fans still feel an element of at best ambivalence, at worst hostility, towards the former Mrs Parker Bowles.

It was for that reason, I think, that the King was determined to see his wife crowned with him. He wants the world to acknowledge how important she is to him, and to accept their deep commitment to each other, a commitment that has survived the test of time and the opprobrium of many.

It was a grand gesture, and an important one. But I think it’s only now, having seen her step up in his hour of need, that people are truly starting to appreciate her qualities. She will always have her critics. But she has worked hard for many years to earn the nation’s trust and forgiveness. This time she truly deserves it.