The legendary photographer says he saw something special in the Brazilian supermodel as soon as he met her when she was a rising star even though others didn't.
He told Grazia magazine: "When I started, Bruce Weber was the Big Star photographer, so all the models were the ones he liked; sporty and outdoorsy. I couldn't find anyone, so I would go to the street looking for people who suited my aesthetic. When I met Gisele in New York, I liked her immediately. No one was using her. I fought for her."
Although Mario, 56, is one of the world's most sought-after snappers, he still worries it could all be taken away from him.
He said: "It wasn't until this September that I felt I had finally arrived. I had six covers and 180 pages of editorial. For once, I felt I was accepted everywhere.
"But I still worry that nobody will call me for the next job."