SARAH VINE: This has been the making of King Charles: Like so many families who face serious illness, the shock and realisation of what's at stake has united the royals

Today's announcement about the health of the King feels like a huge relief, a chink of clear blue sky in an otherwise rather gloomy horizon. After months of games through no fault or desire of his own, King Charles is slowly returning to his duties – just in time to celebrate the first anniversary of his Coronation, on May 6th.

I must confess that when the Palace first announced that the King was suffering from cancer, I – like many – had a sense of deep foreboding. And when the news subsequently broke that the Princess of Wales was also battling the disease, it really felt as though the Royal Family was being pushed to breaking point.

It wasn't just the fact that two of its most prominent and loved members were suddenly seriously ill; it was also that the news came at the end of an already difficult period.

The death of Elizabeth II, preceded by the loss of Prince Philip, the acrimonious departure of the Duke and Duchess of Sussex, not to mention the shame and humiliation of the Prince Andrew affair – it all just seemed to be one calamity after another.

I felt desperately sorry for the King, a man – who for all his past faults – has worked incredibly hard over the years to win back the trust and respect of the British people after the tragedy of what happened between him and Princess Diana.

A charming new image of Their Majesties was released by Buckingham Palace today to mark the first anniversary of the Coronation next week

King Charles waves to crowds of well-wishers from the balcony of Buckingham Palace on his Coronation last May 

Having met and spent time with him personally on several occasions over the years, I have always found him to be a thoughtful man, a little melancholy at times, someone with more self-awareness than those in similar positions usually possess (see Andrew), acutely aware of his responsibilities and incredibly serious-minded about his duties.

He is a kind man too, as we saw at the Duke and Duchess of Sussex's wedding, when he walked Meghan up the aisle in place of her own father, who was too ill to attend.

And when it comes to the harm his youngest son and his wife have done to both him and Prince William, and also to Queen Camilla and the Princess of Wales, he has demonstrated almost saintly levels of composure and patience.

Whatever else he may have done in his life, he is determined to make the most of the immense privilege conferred upon him by an accident of birth and to do some good in the world.

Becoming monarch is not just a rite of passage for him, it has deeper meaning – as anyone who witnessed the solemnity with which he undertook last year's Coronation would attest.

He knows he won't be king for anything like the same length of time as his late mother – but he intends to make his mark and do as much as he can to honour his mother's legacy and secure the future of the monarchy for generations to come.

Charles walked Meghan up the aisle on her wedding to Prince Harry in 2018 in place of her father, who was too ill to attend 

That is why his illness was such a blow. It stopped him in his tracks just as he was starting to get into his stride. It forced him to slam on the brakes and take time out at precisely the moment when he hoped to be going full steam ahead. Apart from anything else, it just seemed so damned unfair.

A lesser man might have succumbed to despondency; but the King has remained relentlessly upbeat throughout this process, staying in touch with current affairs, as curious as ever, meeting with trusted friends and advisors.

He has obeyed his doctors and done what had to be done – but if he has been forced to slow down physically, he has not done so mentally. Indeed, if anything, this illness has focused his mind and made him even more determined to press on with his plans.

And in a funny way, it's been the making of him as monarch – and of Queen Camilla. She has been brilliant at stepping up, not just representing the King but also filling in for the Princess of Wales as she takes time out for treatment. The public have got to know this woman, with her warm smile and sense of humour, far quicker than they might have done otherwise.

We have seen just how much of a team they really are - and the qualities he has always seen in her. And it's also strengthened the King's bond with Prince William and the Princess of Wales who, while still out of the limelight was appointed Royal Companion of The Order of the Companions of Honour this Tuesday on St George's Day.

Like so many families who face serious illness, the shock and realisation of what's at stake has brought them closer together. It's testimony to the King's strength of character and determination that he has faced this trial with such a positive mental attitude.