"You know that his biggest strength without fail is making women look beautiful," said Winslet. "When Mario turns to you and says, 'It's beautiful, but I think it would work better naked, no?' How can one refuse?"
Calling Testino a "magician", Winslet explained that she had no intention of posing naked for the shoot, but was persuaded in a matter of minutes.
"One moment you are in the hair and makeup chair fully clothed and wishing you had smoother skin, longer legs and smaller feet and then Mario comes in and in that charming way he takes you by the hand and says, 'Don't worry it's going to be amazing.'"
Winslet is no stranger to posing naked – she famously appeared nude in the films Titanic and The Reader, but says it's important for young women to know that films and photos aren't a reflection of reality.
"I do think it's important for young women to know that magazine covers are retouched. People don't really look like that. In films I might look glamorous, but I've been in hair and make-up for two hours. With the nudity in The Reader, for example, even I was like, 'Damn, I look good.' It was a bit of body make-up. I don't believe in pretending those things don't go on."
Revealing that her childhood nickname was "Blubber," Winslet admitted to marie claire US in 2009 that she was "always the girl that people would say, 'Ah, it's such a shame, because you've got such a pretty face.'
"I had that well into my teens," Winslet continues, adding, "Even now I do not consider myself to be some kind of great, sexy beauty. I don't mind the way I'm ageing. No reason to panic just yet. I think I look my age, and that's fine."