After Kate's bombshell announcement that she is being treated for cancer I read numerous news reports applauding the 373 per cent surge in internet searches for the word 'cancer'. Incredible, and doubtless this will save lives.

Kate's candour not only encouraged others to seek advice but managed to sweep away any vestige of shame about having the disease. I doubt a single action by a member of the Royal family has ever had such an impact, certainly not since Princess Diana held the hands of Aids sufferers and talked about her struggles with bulimia and her mental health.

But I think Kate's composure will have a more far-reaching effect that will change millions of mind-sets as well.

The Princess of Wales in her video message. 'I was most touched that, on a day when she must have been trembling with nerves and doubtless tired, she had made such an effort with her appearance,' Liz Jones writes

As I watched Kate's video message I was clutching a cushion, strangling sobs that made my throat hurt. And I finally saw the woman behind the immaculate outfits, the composure, the smile. I was most touched that, on a day when she must have been trembling with nerves and doubtless tired, she had made such an effort with her appearance – she had even had her hair done for us. She had got dressed: simply, in jeans and Breton top, but still immaculate. She sat up straight.

Most importantly, she managed a smile. Her concern seemed to be for us, and for her family. She only stumbled on her words once, and that made her seem more human. Her composure reminded me of the late Queen, who could so easily have wailed at the loss of her freedom when she ascended to the throne aged just 25. They both put us first. I'm reminded too of my mum, crippled by arthritis and dementia, but who managed to parrot two phrases, which she repeated to anyone who asked: 'I'm fine' and 'I'm getting better, thank you.'

What a contrast, a revelation, when we are all encouraged to wallow, to own our own sorrow, to 'self care' above all else – a message disseminated by self-help books, podcasts, soothing products and candles.

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Before Kate's video aired, I had just spent a week almost having a nervous breakdown. I was so stressed that I was unable to eat or think straight. I was shaking and sweating, faced with potentially life changing decisions about moving house, moving in with a man, changing my daily routine. I couldn't even take a bath, let alone wash my hair, as what is the point? No one could help me, no one could give me advice. All I could do was escape into mindless TV. I couldn't even focus to read a book: the words danced on the page.

But watching Kate, I realised that the only thing that matters is our health. I once wrote in a column, in a misjudged moment of rage, embroiled in self pity, that I 'would rather have cancer than be made bankrupt. When you have money troubles, no one has sympathy, as they believe it is all your own stupid fault… No one turns up with a pot of stew, or flowers, or help'.

Seeing a young woman – who has three young children, responsibilities – face cancer with stoicism and grace made me feel deeply ashamed. What a whiny nation we've become. Women especially, buckled so easily by cat calling, the menopause, anyone treating us disrespectfully in any way. It put it in perspective that we could be felled at any point by something really serious, and life threatening.

Kate changed my mind-set. It was as though she flipped a switch. We should appreciate each day. Get up, get dressed. I've been a fashion writer for many decades and only now realise that what we wear can be a uniform, a show of strength that changes not only how we appear, but how we feel.

Because if it cancer can happen to Kate – so fit, so healthy, outwardly without a worry in the world – it can happen to any of us. And with our current me me me attitude, very few will be ready…