The Brazilian beauty is now the world's highest earning model but when she first started out the legendary photographer admits her appearance didn't wow many in the industry.
He said: "It was, 'Uh, no, the nose, the waist, the breasts.' They saw problems everywhere. A year later, everyone wanted her."
Over his career, Mario has shot some of the world's most famous people - including Kate Moss and the late Princess Diana - but admits his images haven't always gone down well.
Speaking at Boston's Museum of Fine Arts, Testino - who describes himself as "part psychologist, and part magician" - said: "I've been criticised for pretty, smiley photographs, but at least someone is happy! In my mind, I am always giving the image to the sitter."
Testino - whose clients also include Burberry, Lancome and Britain's Royal Family - also said he has no desire to stop working in the near future as he needs to fund his extravagant lifestyle.
He said: "I can't just have one fabulous thing, I need a hundred. That's why I am always working."