Ever mysterious, "Mona Lisa," one of the world's most famous paintings, may be hiding one more secret. Is she a he? An Italian researchers claims that Leonardo used a young male companion, Gian Giacomo Caprotti, who worked for the Renaissance master as an apprentice, as the model for the work. The young man grew very close to the painter and was likely Leornardo's lover, the researcher Silvano Vincetti says. Other art historians aren't buying Vincetti's story. But in the past, scholars have seen many different faces in Mona Lisa's, including Leonardo's mother and his own self-portrait.