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
It has been suggested that Leonardo created more than one version of the painting. Another contender is the "Isleworth Mona Lisa", which had been hidden in a Swiss bank vault for 40 years before being unveiled to the public on September 27, 2012. The Swiss Federal Institute of Technology in Zurich has dated the piece to Leonardo's lifetime, and an expert in sacred geometry says it conforms to the artist's basic line structures.