LIBBY PURVES: Why George, Charlotte and Louis will be key for Kate getting through the next few months

When life sets you a tripwire, you can't rely on beauty and wealth and fame and titles. You need love and family, self-control and dignity.

In her video statement, the Princess of Wales displayed that rare grace: sitting composedly before the camera, very much herself. She simply gave the facts and wished us well, ending with a kindly hope for others in the same situation.

It felt like an echo of the late Queen in the Covid years saying 'We will meet again'. Indeed, Elizabeth II would be proud of her granddaughter-in-law, and we all should.

Meanwhile, the merchants of fantasy these past weeks should cringe at themselves for all those gleeful speculations about everything from abdication to adultery and bulimia to Brazilian butt-lifts.

Now we know. It's similar news that comes to millions and is always a bombshell. Probably even more so to someone so young, healthy-living, busy and happy.

In her video statement, the Princess of Wales displayed that rare grace: sitting composedly before the camera, very much herself

That first cancer diagnosis forces reconsiderations, rearrangements, altered priorities. For a family woman, a first pressing instinct is to minimise the shock to everyone else, because you realise it's happening to them, too: children, partner, parents, siblings.

When I got my quite sudden cancer diagnosis, I have to admit that my first phone-call to my husband rather uncharitably began 'Now look, don't you come all Yorkshire-gloom at me, but...'.

Any philosophical or frightened reflections about your own possible mortality just have to wait until you have, as it were, stabilised your nearest and dearest.

My immediate family were adults, but when children are involved it must be even more of a priority.

For the Waleses, it must have been infuriating for Kate to be already on chemo, discreetly, during all that ridiculous cardigan-sleeve-photoshop nonsense.

So there's the job of settling the family, and readjusting the diary of work and friendships and holidays, and then there's the actual treatment to face.

I was lucky because I hadn't started to feel properly ill: a vigilant GP and prompt biopsy gave an early warning and, as it was a blood cancer, it didn't mean surgery. But chemotherapy, amazing though its advances are in clearing the little monster cells, is a slog in itself.

Prince William will be a rock for his wife to cling to, but the kids will be the wild surf of life and joy around them both

It must have been infuriating for Kate to be already on chemo, discreetly, during all that ridiculous cardigan-sleeve-photoshop nonsense, writes Libby Purves

I did ask 'What if I don't have this chemo?' To which my cheerful haematologist replied that I might have at most six or eight months. I was, in other words, biologically designed to die sometime in 2020. Oh.

I go a bit laddish at such times, and flippantly said 'Worth a punt then?'. The fine and forbearing Dr Sadullah put it more strongly: my particular one, like many these days, can be 'zapped'.

But having complicated poisons pumped into you is weird. Some get away with pills, but often treatment involves being attached to a drip or, in my case, a tube plumbed into the chest or arm. I spent a week on ward, on a 100-hour drip, then two weeks at home to get over the side effects. Then I returned to the ward for round two - and this cycle continued for five months. While, of course, taking 17 pills a day to counter them, all with dramatic Game-of-Thrones-character names like Domperidone and Acyclovir.

The good news is that the anti-nausea ones are brilliant. The bad news is the interludes of 'neutropenia' - when you're banned from socialising. I used to sneak off to empty cinemas and hide at the end of a row.

Let's hope the Princess gets away with the minimum of medical faff. But it's tiring, boring and frustrating, if your nature is to work and play hard in the full current of life.

If you're a woman, there's usually the gloomy matter of hair-loss to be faced, though the young seem to get it back rather more convincingly than older heads like mine.

Cheerfulness has to be fought for, family jokes nurtured.

I found stupid hats helped me make peace with my reflection in the mirror: the Christmas one with the stuffed model pheasant on top still comes out in memory.

Libby Purves, pictured, says that for a family woman, a first pressing instinct is to minimise the shock to everyone else after a cancer diagnosis

Outsiders' sympathy at such times can feel downright ghoulish. Never ask a cancer patient 'How [itals] are you?' in a soupy voice, with a sympathetic tilt of your head, or rush to stop them doing some job they're perfectly capable of. (My elder brother defiantly painted his boat between treatments.)

So it befits us all to offer the Princess of Wales absolutely no unwanted advice or sentimental sympathy in these coming months, just the odd thumbs-up and cheer.

As for medical privacy, the couple are in an unusual bind: my own instinct was to put my diagnosis on my theatre website at the very start, complete with drug treatment profile, just to bore people from speculating. It worked.

But global royal fame would make anyone quail: the King bravely spoke of his prostate and the Waleses of 'abdominal surgery', and it's their right to leave it at that, while we mind our own business.

The heartening thing is that the very factor that made their task of revelation so tough – their three young children - will make the next months happier.

Children raised in happy affection are not doomy or depressive. They like family jokes, and parents within reach, and chattering about their own enthusiasms. And more jokes.

And when you're down, they have a natural unfussy animal empathy, like a cat that snuggles up when you're feverish or a dog that drops his chewed-up toy on your feet out of pure comradeship.

I am sure Prince William will be a rock for his wife to cling to, but the kids will be the wild surf of life and joy around them both.