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.
Mona Lisa (Prado's version)
The origins of the "Prado's Mona Lisa" are linked to those of Leonardo's original, as both paintings were likely created simultaneously in the same studio. The first documentary reference was made in the 1666 inventory in the Galleria del Mediodia of the Alcazar in Madrid as "Mujer de mano de Leonardo Abince" ("Woman by Leonardo da Vinci's hand"). However, it is still unknown when the portrait entered the Spanish Royal Collection, though it could have been already in Spain in the early years of the 17th century. Since the Prado's founding in 1819, the replica has been part of its permanent collection, habitually displayed in the museum.