Are there two versions of the most famous painting in the world?
Besides the iconic "Mona Lisa" by Leonardo da Vinci that is visited by millions of tourists every year at the Louvre Museum in Paris, there is another similar painting featuring the woman with the famous smile and watchful eyes that has sparked debate among experts over its authenticity.
No one knows where the mystery painting came from when it surfaced more than a hundred years ago in an English country house.
A British man named Andrew Gilbert claims his grandfather purchased a 25% share in the painting in 1964 from a close friend for 4,000 pounds (about $5,200) before it was sold a few times. It has mostly been kept hidden in a Swiss bank vault in recent years, but Gilbert believes his family still has a claim to it.
TODAY's Keir Simmons visited Belgium's Tongerlo Abbey, a medieval monastery, to try to find out more about the mysterious painting.
The Belgian monastery contains what American art historian and da Vinci expert Jean-Pierre Isbouts believes is a second version of another famous da Vinci painting, "The Last Supper." The original is in Milan.
Isbouts believes the other Mona Lisa was also done by da Vinci's hand. Manuscripts and drawings from the time suggest there may have been another version of the iconic painting.
"This painting was discovered in a Swiss vault, and the minute I saw this work I was really blown away,'' he told Simmons. "It took me five minutes and I was convinced.
"The pigments used are the same that Leonardo used in the early 16th century in his workshop."
Isbouts also noted that da Vinci did create two versions of some of his other paintings, including "The Virgin of the Rocks."
Another historian and da Vinci expert, Martin Kemp, disagrees with Isbout's assessment.
"Leonardo, we know, was a terrific fiddler with pictures,'' he told Simmons. "He kept changing. He could always see possibilities. And this is the other Mona Lisa, and this really doesn't have the changes which you'd identify with Leonardo."
There are 15 da Vinci paintings that are officially recognized in the world, five of which reside in the Louvre.
"There are still some other (potential da Vinci) paintings which are still at the center of the debate between specialists," Louvre curator Vincent Delieuvin told Simmons. "It's not easy (to verify them)."