Did Leonardo da Vinci paint two Mona Lisas? Where are they?

Evidently there was a market for erotic paintings. The American art historian David Brown, curator of Italian Renaissance paintings at the National Gallery of Art in Washington, has suggested that da Vinci painted a saucy parody of the Mona Lisa for his patron Giuliano de Medici, and that the Salai version is a copy.

There is only one Mona Lisa, at the Louvre, fully credited to Leonardo. However, there are several Mona Lisa look-alikes from his studio, some of them quite saucy. The one most similar to the Louvre one is the Prado Mona Lisa, a copy made simultaneously in Leonardo's workshop while he painted the Mona Lisa, probably made by an apprentice(s):

La Joconde nue:

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For the one below, art experts suggest that it contains touches indicating that Leonardo contributed to it.

Donna Nuda:

Obviously, the original Mona Lisa also inspired some cheeky versions of her.

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Then there are the ‘meza nuda’ paintings from his workshop, often referred to as Monna Vannas.

Source: St Petersburg. Hermitage, Russia.

While overall similar, there are differences in the shape of the face, the background and other details.

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Source: Chantilly, Musée Condé, France.

Source: Louvre, Paris, France.