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.
Salvator Mundi (Leonardo)
Furthermore, the extraordinary quality of the picture, especially evident in its best-preserved areas, and its close adherence in style to Leonardo’s known paintings from circa 1500, solidifies this consensus.
Yet, there are some respected experts on Renaissance art who question the attribution of the painting to Leonardo. Jacques Franck, a Paris-based art historian and Leonardo specialist, who has studied the "Mona Lisa" out of the frame multiple times, stated: "The composition doesn't come from Leonardo, he preferred twisted movement. It's a good studio work with a little Leonardo at best, and it’s very damaged. It’s been called 'the male Mona Lisa', but it doesn't look like it at all."