An Italian art historian has claimed that the model in Leonardo da Vinci`s masterpiece was one of his male muses, a young man called Gian Giacomo Caprotti, whose nose and mouth bear striking similarities to those of Mona Lisa.
Caprotti, who was also known as Salai, worked as an apprentice with the artist for more than two decades from 1490 and they were probably the lovers, said Silvano Vinceti, president of Italy`s National Committee for Cultural Heritage,.
Some experts had already suggested that Leonardo could have based his masterpiece on a self portrait.
But Vinceti, who has been analysing the painting using state-of-the-art high-magnification techniques, also claims to have found the letter `S` in the model`s eyes, which may be a reference to Salai, the Daily Mail reported.
Several of Leonardo`s works, including` St John the Baptist and a drawing called `Angel Incarnate`, are said to have been based on Salai.
These paintings, Vinceti said, depict a slender, effeminate young man with long auburn curls and almost identical facial features to the Mona Lisa.
"Salai was a favourite model for Leonardo," he said.
"Leonardo certainly inserted characteristics of Salai in the last version of the Mona Lisa."
It has been believed that the model for the Mona Lisa painting, which hangs at the Louvre in Paris, was Lisa Gherardini, the 24-year-old wife of a rich Florentine silk merchant. Experts also believe that Leonardo started painting her in 1503.
But, according to Vinceti, Leonardo might have started painting in the late 1490s in Milan, coinciding with the time he built up a relationship with Salai.
The claims, meanwhile, have caused a stir in the art world, with many dismissing the idea that Mona Lisa was a man.
Pietro Marani, a Da Vinci expert, described the theory of Vinceti as "groundless".
"All Leonardo subjects look like each other because he represents an abstract ideal of beauty. They all have this dual characteristic of masculine and feminine," said Marani, an art professor at Milan`s Politecnico university.
"The work began as the portrait of Lisa Gherardini, but over the years it slowly turned into something else; an idealised portrait, not a specific one.