For the past 30 years, photographer Mario Testino has shot various subjects. But anyone who knew his name would quickly associate him with that engagement photo of Prince William and his then-fiancee Kate Middleton.

In the recent interview with The Telegraph, Testino relates the stories behind his most memorable photos, including that engagement photo of the now Duke and Duchess of Cambridge which he shot a year before their wedding in 2011.

"I waited a long time, an hour or two, to make that picture perfect. But I wasn't totally satisfied," recalls Testino.

"Then, when I'd finished the shoot, they were about to leave and they suddenly hugged in front of a radiator. I took my camera and that was the picture that ran everywhere - it was spontaneous emotion... You could see they were completely in love," adds the renowned photographer further.

Testino went on to describe how Prince William and Kate were as individuals and as a couple.

"Kate, she is beautiful in a different way: she radiates happiness. She is comfortable in her love."

Prince William, on the other hand, was likened to his mother Princess Diana.

"[He] is more like his mother, there's a kindness and a gentleness there that instantly wins you over. [He is] in love with Kate. I knew they would stay together," relates Testino.

Meanwhile, he also recalls his first encounter with Princess Diana, which was a shoot for an auction organized by Christie's to sell off 79 of her dresses. Meredith Etherington-Smith, one of the organizers, was the one who recommended him for the job; though he was a new photographer for Vanity Fair back then.

"I was amazed by this person who, even though she had everything, would go to feed the homeless and visit sick children and Aids victims. It was like a fairy tale. Who was she really? Why did she do this? She was trying to find love. I wanted the world to see her kindness, her humility: I think she realised that would be her way."

The photos that he took of Diana were also featured in a show he held at the request of the Kensington Palace. He invited Princes William and Harry to the event, though he have not met them prior to the show.

"I approached them without knowing them, because I felt that they had to give me their blessing for an enterprise like this. I myself am so close to my mum, I felt I couldn't do anything about their mother without their approval."