ALICE HART-DAVIS: CrossFit, Reformer Pilates... even her kneecaps are lovely! Princess Kate shows a flash of leg as she gets out of her car. But WHAT a leg!

Ooh la la! It's just an accidental flash of leg as a woman gets out of a car . . . but what a leg!

Very pale, very slender, both fine-boned and finely-toned, and it's a leg attached to the Princess of Wales, which makes it all the more extraordinary.

Pictured yesterday while greeting the president and first lady of South Korea on a state visit to London, she appeared to misjudge slightly the height of the car relative to Tarmac and thus the pin of perfection emerged.

Of course, Kate shows us her legs now and then, in daywear that ends above the knee and in shorts on the sports pitch, but these images are far more arresting.

I think it's their contrast to the demure outfit – the chic Jane Taylor hat, the midi-length of her beautiful, £3,000 Catherine Walker red cape coat – chosen to welcome Yoon Suk Yeol and his wife Kim Keon-hee at Horse Guards Parade on the first incoming state visit since the King's coronation.

Kate is on parade with the in-laws and, standing beside William, the coat covers almost to the ankle – though there's a more revealing knee-length dress beneath it. But how does Kate get legs like that? To start with, she's lucky with her genes and body structure, which give her the basic blueprint. Some of us are built like carthorses, and some, like Kate, are nature's thoroughbreds.

She's among the most elegant and beautiful representations of the human form. Even her kneecaps are lovely!

Then there's the fact that Kate is extremely slim. Such low body fat means we can see every detail of her musculature defined and outlined, particularly her calves, slender but strong, their shape perfectly emphasised by her matching £650 Gianvito Rossi heels.

She clearly works out and, in the past, has followed the Louise Parker Method, the lifestyle programme which focuses on daily exercise, three healthy meals a day and plenty of sleep.

But we also know Kate loves sport. Her favourite is hockey, but she's also good at tennis, has the upper body strength for rock-climbing and looks like a natural athlete when she runs. She reportedly enjoys CrossFit, the high-intensity, strength-and-conditioning exercise class.

But, for the key to those exquisitely turned legs, I'd put money on Reformer Pilates, an exercise class conducted on what looks like a wooden torture table.

It's low impact, but delivers a conditioning of the legs like no other – thanks to a specialist machine with a sliding base and all manner of springs to increase resistance. The moves you perform upon this contraption require grace, poise and strength, working all the leg muscles.

The first Reformer Pilates classes arrived in the UK 15 years ago and it has been all the rage ever since.

It's hard work – I know because I used to attend a session in London, trying not to notice supermodels such as Claudia Schiffer or Elle Macpherson on the other side of the room.

But, as Kate perhaps brilliantly displays, it certainly gets results.