It's arguably the most famous painting in the world and few other artworks have been the subject of so much speculation.
For centuries people have questioned the identity of the enigmatic woman in Leonardo da Vinci's "Mona Lisa" painting.
It is only now that media and art experts are picking up on the findings that a German scholar working at the University of Heidelberg first made in early 2005.
"All doubts about the identity of the 'Mona Lisa' have been eliminated by a discovery by Dr. Armin Schlechter, a historian working at the university library," Dr. Sabine Haeussermann, the university spokesperson, told ABCNEWS.com.
"He initially found proof for the woman's identity, when he was putting together old manuscripts for an exhibition in early 2005 and we're still surprised that no one realized the importance of his discovery then, but we're happy to see the reaction today," Haeussermann said.
The historian discovered a margin note by Agostino Vespucci from October 1503 in a book that belongs to the Heidelberg University library. The note identifies Lisa del Giocondo, the wife of a wealthy Florentine merchant, as Mona Lisa.
Lisa del Giocondo was married to Francesco del Giocondo, a successful silk merchant, whose family resided in Florence and Tuscany. It is believed that the painting was commissioned for their new home and to celebrate the birth of their first son.
Schlechter, the historian and manuscript expert at the Heidelberg University library who made the discovery, told ABCNews.com, "Before the discovery, only scant evidence existed who the woman with the mysterious smile might be, but now we know for sure."
"Lisa del Giocondo was first linked to Leonardo da Vinci's work in 1550 by Italian writer Giorgio Vasari, though there had been doubts about his reliability. The margin note in our incunabula from 1503 makes a direct reference and there's no doubt it's authentic," he said.
The historian, who is in charge of about 1,800 "incunabula," books written before 1500, said, "There will never be 100 percent certainty, but based on what we know today, even renowned Leonardo da Vinci specialists agree that the painting is a portrait of Lisa del Giocondo."
He's also quick to point out that he would never have made the discovery without the real historic document being physically available for his research on the subject.
"Despite all efforts to improve the digitalization of historic documents, specialists will always need to maintain in close touch with the real thing — the original incunabula or books — or else a lot of historic facts may remain undetected."
The painting, also known as "La Gioconda" in Italian, or "La Joconde" in French, is a 16th-century portrait painted in oil on a poplar panel by da Vinci during the Italian Renaissance. It is probably the most valuable painting ever insured, according to the Guinness World Records, and tens of thousands of visitors flock to the Louvre in Paris each year to see it.