Diana 1961-1997: No matter what outfit, the woman underneath shone through

When British Vogue featured the Princess of Wales on the cover of the magazine in July 1994, who could resist the black and white portrait by Patrick Demarchelier and the simple cover line: "Happy Birthday The Princess of Wales. New Portraits".

Here was Diana, aged 33, with the sad but smiling eyes, with the beginnings of a few crow's feet. Other celebrities would have insisted that every line or crease was retouched to a smooth glow. But not Diana. That was the essence of her style. Here was a woman at the pinnacle of beauty and glamour, a Vogue cover girl; yet every woman could relate to those small wrinkles. She was not super-humanly perfect. She always looked real and approachable.

Diana's style was a natural one. She was just as at home in a couture ball gown at a state ceremony as she was in her gym kit, or with windswept hair and bullet-proof waistcoat on the minefields of Angola. Her style evolved slowly from the days of her engagement to be married when she wore the frumpy pie-crust frills of a teenage Sloane Ranger. The Emanuel wedding dress was that of a fairytale princess and was the start of one of many close relationships with British designers.

That was also the point at which she inspired other women to dress like her. The style of that wedding dress, give or take a few metres off the train, was imitated by brides across the world. Over the years, women have copied the Diana hair, slicking it back when she slicked hers and hiding under their fringes when she did the same. One particular hairdo in February 1995 dominated every tabloid front page. The papers didn't like it. The style was not feminine enough. But women rushed out to buy a tube of hairslick to try it for themselves.

Unlike Jackie Onassis, who led trends and was at the forefront of fashion in the Sixties, Diana was a staunch classicist. She stuck to her own wide- shouldered suits, the sapphire and diamond earrings, the evening frocks that often made her look old before her time, and the matching shoes and bag. Even her make-up - the slightly smudgy eyeliner and the natural lips - remained the same throughout the years.

She was not a woman at fashion's cutting edge, as her recent charity sale of eighty dresses at Christie's in New York highlighted. Some of the dresses were ruched and gathered to the point of monstrosity. Others, like one embroidered ballerina dress, were simply cut to an unflattering length.

However unfortunate the style of dress, it was the woman beneath the drapes and ruching that always shone through. She was the sort of woman who could have worn a sack and still looked fabulous. No wonder designers fantasised about dressing Di. She had everything - the height, the even features, the legs and those well-toned, statuesque shoulders worthy of any supermodel.

As well as supporting British designers such as Elizabeth Emanuel, Zandra Rhodes, Bruce Oldfield and Catherine Walker, Diana was also courted by designers including the late Gianni Versace whose memorial service she attended in July, and by Bernard Arnault, the owner of luxury goods conglomerate, LVMH.

It was he who persuaded the Princess to wear the first dress for Christian Dior by John Galliano last December. No other woman had the power to generate so many front pages across the world for the sake of one navy dress. She could not do anything to her appearance without comment from the newspapers. She was every designer's dream.

"Perhaps one day she'll come to me," Vivienne Westwood told Woman and Home magazine in 1995."You'd see some results. I could make her the most stylish woman in the world." Westwood had criticised the Princess for being "ruled by trends" She said: "It's as though her clothes are supposed to tell you she's both a feminist and sexy at the same time. It's a compromise - and it doesn't work."

It was precisely the fact that she was a woman trying to control her own life, acknowledging her position as a role model to other women, while not being afraid to wear a one-shoulder dress or a skirt split high up the thigh that made Diana so alluring. Nobody was pulling her strings either in her choice of dress or the way she chose to lead her life.

Beyond her strong physique was a personality that no amount of money or plastic surgery could buy. Tall, slim, and graceful, she could carry off whatever she wore. She also knew how to be photographed. From the early days when she could barely lift her kindergarten-teacher chin high enough for cameras to see her face, she became as skilled as a movie star or fashion model at loving the camera lens and making it love her.

As well as two covers for British Vogue - both promoting charities - and one for American Vogue when the journalist Georgina Howell followed Diana on a Red Cross trip to Kathmandu, and another for Harper's Bazaar, Diana's most recent cover was for Vanity Fair in July.

The photographs showed a woman relaxed, warm and at ease with the camera, laughing flirtatiously with the fashion photographer Mario Testino. And as usual, Diana was using her style and her image, not only as the mother of the future King of England and tireless charity worker, but that of Diana as fashion and lifestyle celebrity, to promote the sale of her dresses at Christie's.

She was only too aware of the power of a set of portraits. Proceeds of the non-profit making sale went to Aids Crisis Trust, The Royal Marsden Hospital Cancer Fund and other related charities in America.

Diana's style was at its best when, as for those Vanity Fair pictures, she was at her most relaxed, natural and dressed down. She suited nothing better than a pair of jeans and a crisp man's white shirt. How thoroughly modern of her to own about 30 pairs of jeans - Rifat Ozbek, Armani and Versace as well as good old traditional Levi's were among the labels on the waistbands.

The key to her style was not baubles, spangles and big frocks. It was the pared-down style of the modern career woman and mother of two that made her stand out. Hers were the sort of clothes that Every woman could relate to - and in fact wore in day-to-day life.

Days out with her sons would be spent in a sweatshirt, jeans and baseball cap. One of the most enduring images of Diana is in her aerobics gear en route from the gym in shorts and a sweatshirt. The most recent pictures of Diana on holiday showed a tanned woman in vest and jeans shorts or with her hair pushed up into a baseball cap. Like everyone, she could have a bad hair day and hide it under a cap.

Diana's true style only began to come into its own over the past four years, since the separation from Charles. She asserted her independence by moving away from frills and flounces and into a cleaner, sharper more contemporary way of dressing.

However, it is the woman within, rather than the clothes she wore, that will always shine through.