(Image Credit: Mona Lisa Foundation | Getty images)

It's a mystery straight out of the da Vinci code. A famous portrait, hidden away in a Swiss bank vault for 40 years, with the potential to break open a mystery more than 500 years old. A second, earlier version of the Mona Lisa was unveiled to the public today, a version that experts say they can prove is the work of the master himself.

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.

During WWI, the painting was moved to America for safekeeping. The portrait eventually made its way back to Europe, where it was analyzed in Italy before being sent to the Swiss bank vault for safekeeping. Since that time, experts from the non-profit Mona Lisa Foundation have been working to prove or disprove the portrait's authenticity

"When we do a very elementary mathematical test, we have discovered that all of the elements of the two bodies - the two people, the two sitters - are in exactly the same place," art historian and foundation member Stanley Feldman told The Associated Press.

"It strikes us that in order for that to be so accurate, so meticulously exact, only the person who did one did the other. … It's an extraordinary revelation in itself, and we think it's valid."

Such similarities aside, the two Mona Lisa's have many notable differences, the Isleworth version is larger and features columns on either side of the figure, believed to be Lisa del Giocondo. The version that hangs in Paris' Louve Museum is narrower and features no such columns.

The Isleworth painting was done on canvas, while the Louvre painting, which features a far more detailed background, was done on wood. The woman in the Isleworth version also appears younger than she does in the Louvre, leading to the theory that the portrait might have been painted earlier, consequently featuring a younger del Giocondo.

The foundation's claims aside, many in the art and scientific community remain unconvinced.

"It's a perfectly honest, well-made early copy," Martin Kemp, an Oxford University professor and da Vinci expert, told ABC News today. "Pictures were copied [because] you couldn't go to the Internet and order a reproduction. So if you wanted something like that ['the Mona Lisa'] and you couldn't get a hold of a Leonardo, you would order a copy."

With the debate still raging, it is difficult to reach a definite conclusion about the painting's authenticity. So, until the foundation releases more evidence, it looks as though experts will be left to speculate about whether the Isleworth Mona Lisa is the work of the Renaissance man himself, or one very gifted Impressionist.