It opens on July 14 and draws on the gallery's collection of more than 40 images of Diana, some of which have never been publicly displayed.

Paul Moorhouse, curator of 20th-century art at the gallery, is responsible for the show. He says the works cover the period from 1981 to 1997 - from her marriage to Prince Charles, aged 20, to her death in a car crash with Dodi Fayed after being chased by paparazzi.

The images were taken by 11 photographers: Lords Snowdon and Lichfield, Carole Cutner, David Bailey, Terence Donovan, Derry Moore, George Grimes, John Swannell, Roger Hargreaves, Jose Manuel Ribeiro and Mario Testino. The Testino photos were the result of her last official shoot.

'The display goes through various phases,' Moorhouse says. 'It presents the young Diana by Snowdon and Cutner in 1981. Lichfield's pictures depict her marriage to Charles, and there's an interesting Terence Donovan photograph where Diana is portrayed as a private person - it's a very intimate photograph. The tension between the public figure and private individual is something we wanted to explore. This leads us to a photograph with Charles taken in 1987 by Terence Donovan which suggests some of the tensions creeping into their marriage.

'We see her evolving into a figure associated with style, and the David Bailey pictures portray both the mature Diana and the icon of fashion.'

Also on display are a shot of a thin-looking Diana that hints at her anorexia, one from her charity work, and one of her as a mother - the photograph of her with William and Harry by Swannell.

Then there are the final Testino shots, in which she looks completely relaxed. Moorhouse says the exhibition charts her development into an assured public figure.

Diana was one of the most photographed women of recent times, and a charismatic figure - although it's hard to explain why she continues to attract such attention 10 years after her death.

Moorhouse says that behind the public persona was a fragile individual, and that people could sense the tension.

'One also thinks of Marilyn Monroe,' he says. 'She commands a similar fascination. And both had a tragic death. Before Diana, the royal family was a rather inscrutable institution and the images seen by the public were rather formal. But she rewrote the rules. She was an individual - not just the Princess of Wales, but Diana the woman. And she was able to keep both in play. She also had an effect on how we see the royals today.'

Diana's evolving relationship with the cameras can be seen in the photographs. In some early shots she looks shy and awkward, as in Cutner's 1981 shot, which shows her wearing a simple pink cardigan, with little makeup and her hair unstyled.

In Snowdon's 1982 shoot for Vogue she appears almost angelic, and for Donovan's 1986 portrait she wears a long, dark, velvet dress and looks rigid against a studio backdrop. She would later describe feeling 'hunted' by the paparazzi (Hargreaves shows her walking past a bank of snapping photographers), but in the later images she looks to be in control.

Sitting for Bailey in 1988 she seems self-assured, smiling comfortably as she leans against a post wearing a v-necked top, leather belt and figure-hugging black skirt.

But it's with Testino that she looks most comfortable. 'She undoubtedly learned to use the media to her advantage in the end,' Moorhouse says. 'It was a double-edged relationship. On the one hand, she felt hunted, but she was also a skilful manipulator. And this comes across in these works. She went from being a shy, withdrawn individual to a woman who felt relaxed and confident. They were two entirely different aspects of her character.'

Diana, Princess of Wales, National Portrait Gallery, Jul 14-end of Oct