Isleworth Mona Lisa
According to Leonardo's early biographer Giorgio Vasari, Leonardo had started to paint "Mona Lisa" in 1503, but "left it unfinished". However, a fully finished painting of a "certain Florentine lady" surfaced again in 1517, shortly before Leonardo's death and in his private possession. The latter painting almost certainly is the one that now hangs in the Louvre. Based on this contradiction, supporters of the authenticity of the "Isleworth Mona Lisa" claim it is the unfinished "Mona Lisa", made at least partially by Leonardo, and the Louvre "Mona Lisa" a later version of it, made by Leonardo for his own use.
Speculations about Mona Lisa
Maike Vogt-Lüerssen argues that the woman behind the famous smile is Isabella of Aragon, the Duchess of Milan. Leonardo was the court painter for the Duke of Milan for 11 years. The pattern on "Mona Lisa's" dark green dress, art critic Maike Vogt-Lüerssen believes, indicates that she was a member of the house of Sforza. Her theory is that the "Mona Lisa" was the first official portrait of the new Duchess of Milan, which requires that it was painted in spring or summer 1489 (and not 1503).