Above is Leonardo da Vinci's 1499 sketch of Renaissance patron Isabella d'Este, and until recently, art historians did not believe Leonardo ever got around to painting her portrait.
The 500-year-old mystery may have come to an end when a finished painting, which looks remarkably like the sketch, was found in the Swiss bank vault of an unidentified Italian family.
The Telegraph reports that, "Art historians had long believed he simply ran out of time — or lost interest — in completing the commission for Isabella d’Este."
A number of scientific tests confirm that both the date and pigments used suggest that the painting is authentic. However, there are some concerns that the painting may have been the work of one Leonardo's pupils.
The sketch version is currently hanging in the Louvre.