Mario Testino: First Diana, now Camilla

The man who took the last portraits of the Princess of Wales tells Hermione Eyre why he wants to photograph the woman who followed her as wife of Prince Charles

Nightfall at Kensington Palace. Mario Testino is guiding me through the royal apartments. We tiptoe through the plush, red rooms, half-lit and heavy with state. Then we round a corner, and there she is: Princess Diana, laughing. Six enormous prints of her, ranged over bright white walls. Diana with her hands on her hips; with her head on one side; in profile; smiling. Testino turns to me. "The first time I saw these here, there was a knot in my throat."

The photographs are from Testino's famous session with the Princess in 1997. It was her last shoot, taken six months before she died. Testino selected some of the photos and sent them to Diana - she told him that her sons said they were "the most like her they had seen". The best ones were published in Vanity Fair and became central to Diana's myth and her iconography. But the leftover shots from the session have not been shown publicly before this exhibition. Instead, they have been languishing in Testino's London archive. "I had to wait for the right moment," he says. "Now Kensington Palace has invited me to do this, it feels right. It's almost 10 years since she died. It's time to celebrate her life."

To this end, the exhibition is bright, flashy - blinging, even. The designer Patrick Kinmonth and the wallpaper house Coles have been hard at work. They have taken the contact sheets of Diana posing during the Testino session, stylised them into a sort of potato print, and turned them into shiny silver wallpaper. One small room of the exhibition is entirely papered with this design. It resembles a stalker shrine as designed by Andy Warhol. "But this is her sense of fun, her style, no?" says Testino. "She would have thought it was a scream."

Testino flops into a baronial chair (designed for the exhibition by Kinmonth, it features two intertwined "D" shapes). He is quick to admit he was not "best friends" with the Princess. "We met three times, exchanged a few letters, phone calls. We had one portrait session." But the rapport they established shines through the photographs.

Was there a large entourage there, I ask. "Team", he interjects. "I prefer team." Or was it a one-to-one? "There was hair and make-up, too, and a stylist. She really put herself in their hands, which was amazing."

In one shot, I notice that Princess Diana is laughing as if she is looking at someone doing something silly. Mario? "Yes," he sighs. "I was dancing." He wiggles his hands in demonstration. "I put on this CD of a disco version of the Seventies French singer Dalida. Diana said she couldn't dance like me - 'I'm not Peruvian,' she said. She simply swayed a little. It was lovely. My idea as a photographer is not to try and change people, but to embrace and emphasise the style they have."

It could be this sympathetic approach that has won Testino sittings with people ranging from Madonna to Queen Rania of Jordan via Gwyneth Paltrow. But their patronage might equally have something to do with the flawless look Testino gives them. He doesn't see beauty in truth; he sees truth in beauty.

Like Joshua Reynolds before him, he would rather create an image than capture a reality. "People want to work with me because I make them look good," he has said. Here in Diana's former home, at night, with her face beaming from every wall, it seems rude to analyse what airbrushing, what nips and tucks Testino has made to these prints. There has been ample opportunity: he has "remastered" them from film negatives to digital prints. "I don't change anything essential," he protests. "I am not in favour of retouching the form, the silhouette. People need to retain their identity. Why would I want to make Kate Moss look like Gisele Bundchen?"

After this neat change of subject - he is a born courtier - Testino proceeds to eat several measures of a horrid-looking green powder."Homeopathic medi-cine," he explains. "For the occupational injury done to my arm." Testino, it seems, is suffering from Snapper's Elbow. Tall and tanned and slender, he is boyish yet no longer young. He waves his reading glasses sadly at me as proof. And his index finger is badly crooked. "I have sacrificed my body to photography," he laughs.

Testino, 52, has been the most prominent portraitist in the world for close to a decade. His lifestyle - he takes on average 200 flights a year - is surely unsustainable. And ecologically unsound? "Oh God, I don't think of that," he says. "I adore aeroplanes because they give me a chance to rest." But where will he make his home when he finally settles down?

"I will come back to Peru. This is where my family is, where the people who will care for me when I am old and sick are. Hopefully it's not going be too soon, though. I always want to keep a base here in London."

Testino's family - as we know it - extends to his older sister and his 83-year-old mother. He has never spoken publicly about lovers or partners. Ambiguity on this front appears important to him.

"I would love to be here more, but I only have two clients: Burberry and British Vogue. Otherwise, the work is simply not here for me." He gives amoue. He's also a little discomfited by the British press's treatment of Kate Moss. "It's hard to say, but the whole situation was a little ..." Cruel? I offer. "Cruel," he concurs. "It's not that the blame should be absolutely on the media, since it's the public's desire to buy these magazines, isn't it? That directs the way they report it. But it was not kind. You know, she hasn't been back here since," he adds, pointedly.

But what of Testino's recently expressed desire to photograph Camilla, Duchess of Cornwall? Isn't it a little, well, disloyal to Diana? "Why?" he says, lightly. "Time goes by. I would love to photograph her. She is a very good-looking woman. And very charming. So many of my friends have separated and remarried and I remain friends with their ex-partners even if they no longer speak. Prince Charles has the same right as any other man to be happy. I've photographed him a few times, and since his wedding he is ... just a happy man. Why deny that to anyone?"

We are interrupted by members of his entourage - sorry, team - who need his help putting the final touches to the rest of the exhibition.

Testino heads through the Warhol chamber (where yet more photographs of her will rotate on a plasma screen) into a room covered in dust sheets and smelling of fresh paint. Here, Diana's dresses stand arranged in a sealed case.

Looking at the photographs from a distance, I ask casually why one was taken from a different angle from the rest. "I was crouching down there because I was changing a film," says Testino. "Because someone else was changing your film, more like," says one team member, cheekily.

Testino laughs. "I used to have to do everything myself, you know. I've come a long way, baby."

Diana, Princess of Wales by Mario Testino, a new exhibition of photographs and dresses, opens at Kensington Palace, London, (0870 751 5180) on Thursday

BIOGRAPHY

Born: 1954 in Peru to a family of Irish, Spanish and Italian origins, he was raised in the affluent part of Lima. As a young boy he would accompany his father, who worked in property and oil, on business trips to New York.

Education: Attended the American School of Lima. Studied economics at the Universidad del Pacífico, law at the Universidad Católica and international relations at the University of San Diego, California - and dropped out of all three.

Career: His first ambition when he came to London in 1976 at 21 was to be a priest.

Lucky break: Lucinda Chambers of British Vogue spotted his talent when he was broke.