(Image Credit: Jean-Pierre Muller/AFP/Getty Images)

The Mona Lisa: It's one of if not the most famous piece of art in the world. Leonardo da Vinci's masterpiece has inspired numerous forgeries and impersonators but none of them can compare to the original, which hangs in the Louvre Museum in Paris.

None of them, that is, except for the true original Mona Lisa that was painted by da Vinci roughly 10 years earlier. That's right, the Mona Lisa might have an older sister.

Known as the Isleworth Mona Lisa, the painting was discovered shortly before World War I by English art collector Hugh Blaker, who purchased it from the noble family to which it had previously belonged. Blaker then moved the painting to his studio in Isleworth, England, giving it its iconic name.

The Islesworth Mona Lisa is slightly larger than the one that hangs in the Louvre and is framed by two columns. It has also been noted that Lisa del Giocondo, the woman who posed for the portraits, appears younger in the Isleworth version, lending credence to the theory that it was painted earlier.

Although compelling, such evidence is far from proof that Isleworth Mona Lisa is anything more than a convincing forgery. The painting's authenticity has been subject to furious debate among art historians and collectors, until now.

The Mona Lisa Foundation, which was set up to conduct research into the work, has announced that it has "historical, comparative and scientific evidence" that will prove once and for all that the painting is an authentic de Vinci.

Professor Carlo Pedretti of the Armand Hammer Center for Leonardo Studies at the University of California in Los Angeles and professor Alessandro Vezzosi, director of the Leonardo da Vinci Museum in Vinci, Italy, have lent their support to the claim. But until the foundation unveils its new evidence, the painting will remain as mysterious as the source of the Mona Lisa's smile.