For centuries, people have been speculating about who modelled for Leonardo da Vinci's Mona Lisa. Now, an Italian art historian has claimed that the model in the world's most famous painting is in fact a male and not a female. According to Silvano Vinceti, the Renaissance artist's male apprentice and possible lover Gian Giacomo Caprotti was the main inspiration for the masterpiece.Caprotti, also known as Salai, was one of his male muses.