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
In 2004, historian Giuseppe Pallanti published "Monna Lisa, Mulier Ingenua" (published in English as "Mona Lisa Revealed: The True Identity of Leonardo's Model"). The book gathered archival evidence in support of the traditional identification of the model as Lisa. According to Pallanti, the evidence suggests that Leonardo's father was a friend of del Giocondo: "The portrait of "Mona Lisa", done when Lisa del Giocondo was aged about 24, was probably commissioned by Leonardo's father himself for his friends as he is known to have done on at least one other occasion." In 2007, genealogist Domenico Savini identified the princesses Natalia and Irina Strozzi as descendants of Lisa del Giocondo. Scan data obtained in 2004 suggested that the painting dated from around 1503 and commemorated the birth of the Giocondo's second son.