It's twenty years since Kate was first snapped with Wills and a tidal wave of unfair criticism began. But I know why she'd do it all again, writes ANGELA MOLLARD

The Prince and Princess of Wales have plenty of other things to think about right now, but to their legions of fans, the start of April has a very particular significance.

Because it's two decades this week since the world first learned that William, heir to the throne, and a 22-year-old commoner, Kate Middleton, were boyfriend and girlfriend.

They'd been photographed smiling and nestling against each other as they rode a drag lift up the slopes at the Swiss skiing resort of Klosters.

And on April 1, The Sun published the picture as a world exclusive with the headline 'Finally, Wills gets a girl' – which might suggest more about the newspaper's impatience with the young Prince's love life than his pulling power.

Looking back today, it's clear that any concerns about William's romantic tardiness were hopelessly misplaced.

Because in those images there is evidence of the same closeness and care that the couple still exhibit two decades on. He was waiting to choose, in other words – and chose wisely.

Kate and William might have looked like any other young couple in love back then, but you can also detect a protectiveness in the young prince, a quality that his wife will be drawing upon now more than ever.

Perhaps it's instinctive, a natural response to knowing that any woman he showed interest in would find herself in the spotlight.

Or maybe it's a trait that originally developed through wishing to protect his late mother, Diana.

Whatever the case, the gentle tilt of William's head tilt in those first photographs betrays a kindness that Kate will be relying upon like never before as she faces her battle with cancer.

Twenty years is a big chunk of time, particularly in a royal context.

It's longer than the late Princess Diana was at the forefront of public consciousness and it's longer than King Charles and Queen Camilla have been married.

But what's also remarkable about the photographs from this and other skiing holidays is how happy Kate looks.

It's a reminder of how we have rarely seen her without a smile.

Back then, we could hardly have known that the pretty brunette from a decidedly middle-class background possessed exactly the characteristics which would enable William and Kate to establish the most solid royal marriage since the late Queen Elizabeth fell for the dashing Philip Mountbatten.

With the Royal Family seeming more fragile, more human, than any time in recent memory, it's that relationship that the Prince and Princess of Wales appear to be emulating as they navigate these worrying days.

When Kate spoke of William being 'a great source of comfort and reassurance' as she revealed her cancer diagnosis to the world, her words were reminiscent of Queen Elizabeth's loving tribute to the husband she described on the occasion of her Golden Wedding in 1997 called her 'strength and stay'.

At a time when the House of Windsor has two of its key principals out of action, the strength and solidity of the Wales's marriage is a stabilising force of huge importance.

That picture from two decades ago reminds us that William and Kate, health willing, will be the emblematic figures of the century ahead, just as the Queen and Prince Philip were central to the one before.

Unlike the marriage between Charles and Diana, which imploded in front of our eyes, there hasn't been a single photograph of Kate and William in 20 years which suggests anything other than shared purpose and love.

Whether working alongside one another or attending engagements as a family with George, Charlotte and Louis, theirs is a union built to last.

Even when they split briefly as boyfriend and girlfriend in 2007, they quickly reconnected. As Kate said afterwards, she wasn't happy about it, but the experience made her stronger: 'You find out things about yourself that maybe you hadn't realised.'

We can never know for certain what takes place inside someone else's marriage but that statement indicates not just resilience, but a willingness to grow.

Likewise, Kate's determination to take responsibility for the Photoshop errors in the family picture released on Mother's Day shows another strength – an acceptance that people - even the royals - can sometimes get it wrong.

After a memorable five years in which some members of the Royal Family have seemed unable to reflect upon their own actions - and have instead blamed others - the princess's smooth and speedy apology spoke volumes.

From the label 'Waity Katie' to author Hilary Mantel's damning assessment of the princess as a 'shop-window mannequin' selected only for breeding, Kate has weathered her share of often very unfair criticism over time.

But when it started coming from the brother-in-law she'd once adored and his indignant wife, it must have been still harder to bear.

Had 22-year-old Kate Middleton known she was going to shoulder such abuse - including unfounded claims of racism - plus the suspected breaches of her medical records and social media speculation so frenzied she was forced to share her private suffering with the nation - would she have stuck with the young prince on the ski lift?

My answer is: undoubtedly.

Because Kate's secret weapon has always been that steeliness behind the smile.