RICHARD KAY: The double whammy of King Charles and the medical treatment of our future Queen Kate leaves the nation reeling… it sends a shiver down our spines and shows how worn out the royal resources are

For women everywhere, she is as celebrated for her beauty and poise as for her smiling, vibrant energy. A youthful mother whose slim figure and lustrous hair seem the essence of good health.

The news that the Princess of Wales has undergone abdominal surgery and will remain in hospital for two weeks is therefore very shocking.

Following the grief over the late queen's slow decline and death, the bulletin about Catherine has sent a collective shiver down the spines of royal fans. People falter.

No sooner had the announcement sunk in than it was revealed that the king would also be admitted to hospital for treatment of an enlarged prostate.

Never before has there been a double dose of royal medical bulletins to remind us of the fragility of the human condition.

But while the King, at 75, is at an age where such procedures can be expected and faced, Kate radiates youth and grace.

She is 42, a birthday she reached just last week, but given her muscular and slim figure, which keeps her in excellent shape while running in Windsor Great Park, she could pass for someone ten years younger.

Everything she does seems to require no effort at all. And yet she is a future queen who, it is fair to say, has secured the long-term future of the monarchy – not just through her three beautiful children, but through that indispensable brand of Middleton magic she has brought to her marriage.

Perhaps her greatest quality is steadfast stability. Never has that been more important than at the start of a government plagued by the twin threats of the bitter Prince Harry and the scandalous Prince Andrew.

And it is because so much seems to be riding on this Home Counties girl, whom Prince William first noticed on the St Andrews University catwalk more than twenty years ago, that the unexpected revelations about her medical condition are so have been baffling and, indeed, disturbing.

Kate is not only the glue of her own immediate family, but also the smiling figure supporting a royal family that she has given a much-needed modern twist

She rarely puts a step wrong and has quickly learned to avoid the pitfalls of a public life where appearance and presentation are everything.

She exudes just the right mix of warmth and discretion, sharing an unguarded glimpse of life as a royal wife without exposing herself or her family more than is right or, frankly, necessary.

From the saddest state events such as the funerals of Prince Philip and the Queen to the glory of the Jubilee and Coronation, she exudes calm, confidence and tranquility.

As the mother of George, Charlotte and Louis, she broke the mold and rejected the Windsor traditions that required her children to be confined to a boarding school.

Even Princess Diana, despite all her revolutionary zeal, could not achieve that.

And she's done all this without relying on the legions of flunkies that normally make up a royal household.

This is why Prince William obviously has a tough few weeks ahead of him, perhaps with school tasks, organizing bath time and reading bedtime stories.

Thanks to Kate, the three children enjoyed a childhood where two parents shared the duties, very different from William's own experiences at Kensington Palace.

Unsurprisingly, aides were keen to make it clear that in between his time at his wife's hospital bedside, William's priority will be the children rather than royal duties – a refreshing and welcome change from the past.

Planned trips to Latvia and later to Rome and the Vatican will therefore almost certainly be postponed.

The news of Kate's admission to the London Clinic and of the proposed treatment for the king has also highlighted how scarce royal resources really are.

Since neither Andrew nor Harry can be called upon, it means that running the royal show depends on Princess Anne and her brother Prince Edward.

No wonder Anne recently pointed out that there was not much room to further slim down the monarchy.

For now, the focus is on Kate as she recovers from surgery. Kensington Palace declined to release further details other than to say it was unrelated to cancer, although she added that she would need several months to recover and was unlikely to resume public duties until after Easter.

Her absence will be felt everywhere, for she is a woman on whom so much and so many depend.

It's not just William who hopes she can return to her place at his side with that shining zest for life. That also applies to all of us.