The book is edited by Patrick Kinmonth, long-term collaborator and friend of Testino's. The selection of about seventy photographs includes many unseen images which, alongside previously published images, fill in the untold story of the shoot. The book brings together the most beautiful images from this last portrait sitting, displaying Diana in a state of relaxation and intimacy unlike any other. Just five months before her tragic death in August 1997, Diana Princess of Wales was photographed by Mario Testino for Vanity Fair.

It showed, I think, in the photographs.Inside Princess Diana's last portrait session. I got a letter from her shortly afterwards saying that the shoot in the old Battersea schoolroom had been one of the happiest days of her life. It was absolutely brilliant and we were all crying with laughter and applauding. Not to be outdone, the princess then leapt to her bare feet and did a very convincing Naomi Campbell prowl, followed by a Bardot-like Claudia Schiffer. Mario is a brilliant mimic and he catwalked from one end of the studio to the other, taking off the very different styles of various top models. During lunch the talk turned to fashion shows and catwalk models.

I had organised a delicious cold picnic which we all ate together round the scarred ex-schoolroom tables. But my brush with greatness really started over lunch. When the photographs appeared in Vanity Fair in 1997, they made history – no one had ever seen the princess look natural, fun and modern in the way that Mario revealed that day. Her make-up and hair would be kept to a natural minimum to suit the new non-ceremonial life she had started to lead – and her extraordinary natural beauty. She’d be in simple, modern clothes with no jewellery. She wouldn’t be heavily made-up, jewelled and tiara’d in the stiff ballgowns of her royal life. We were there to shoot some pictures to show the Princess in a new light.

I remember she was wearing a very sharp little black and white houndstooth suit which had been the star of John Galliano’s recent show for Dior, and even though she had hardly any make up on she looked wonderful – slightly pink and gasping from all the stairs she had negotiated. Then, through the doorway came a couple of hands clutching dress bags rather insecurely, and Princess Diana almost fell into the studio.

Diana testino