Two questions have haunted the Mona Lisa since Leonardo da Vinci painted it 500 years ago. Who is she? And why is she smiling? A German researcher claims to have found final proof of her identity.
Deep in the archive of Heidelberg University, researcher Veit Probst says he has found a book that once belonged to Agostino Vespucci, a friend of da Vinci.
In the margin of one page is a note from October 1503 which, the researcher claims, confirms the identity of the Mona Lisa as the Mona (for Madonna) Lisa del Giocondo, the third wife of a Florentine businessman Francesco del Giocondo.
She was always considered the most likely subject of the work, painted between 1503 and 1506. Without definitive confirmation, however, the mystery around the work grew, making the grand lady of the Louvre the most famous portrait in the world.
The first conspiracy theories began to surface as soon as the diminutive oil painting had dried. If it really was a portrait of Lisa de Giocondo, commissioned by her husband, why did the artist not hand over the painting on completion? Da Vinci kept the portrait with him and only sold it shortly before his death.
The rumour mill gathered pace: the portrait was a picture of Jesus Christ, or of Mary his mother, or Mary Magdalene. No, it was a picture of a lover of da Vinci. Perhaps a portrait of da Vinci's mother?
Some were sure that the Mona Lisa is a self-portrait of da Vinci in drag. It would certainly explain the smile.
But Probst says he will burst all these conspiracy balloons in a forthcoming essay. He has independent verification that the Vespucci note is genuine and thus, he says, contemporary proof that the Mona Lisa was, well, the Mona Lisa.
Like the best puzzles in Dan Brown's The Da Vinci Code, the identity of the young woman in the painting was in plain view: in Italian, the work is known as La Gioconda.
Even if we now know for sure who she is, the Mona Lisa still clings to her final mystery: why is she smiling?