Photographers crowded round as the curtain was pulled back to present what is claimed to be an early version of Leonardo da Vinci's Mona Lisa.
But even the experts brought in by the non-profit Mona Lisa Foundation in Geneva, Switzerland, were not sure about that claim yet.
The art world is prone to rumour and speculation, but a new claim about the world's most famous painting, which draws millions of visitors to Paris's Louvre Museum each year, has caused a fuss.
The "Isleworth Mona Lisa" features a dark-haired young woman with her arms crossed against a distant backdrop. The foundation insists it is no copy but an earlier version of the Louvre masterpiece.
At the presentation, Alessandro Vezzosi, director of the Museo Ideale Leonardo da Vinci, said the painting was intriguing but needs further study. He declined to line up behind the foundation's claims that it was truly a "Mona Lisa" predecessor painted by da Vinci.
Ever since the 16th century, several historical sources suggest that da Vinci painted two "Mona Lisa" versions. One was of Mona Lisa Gherardo around 1503 that was commissioned by her husband, Francesco del Giocondo, the foundation said. Another - the one in the Louvre - was completed in 1517 for Giuliano de Medici, da Vinci's patron.
That theory fits with da Vinci's tendency at times to paint two versions of some of his works, like the Virgin of the Rocks, the group said. The foundation acknowledged that the "Isleworth Mona Lisa" remains unfinished, and that da Vinci did not paint all parts of the work.
The Isleworth painting first came to public light after British art collector Hugh Blaker found it in a home in Somerset before the First World War. Blaker bought the painting and took it to his private studio in Isleworth, in west London.
US and British newspapers speculated even then that it might be a da Vinci, but at that time only art experts - not high-tech science tests - could judge.
During the Second World War, Blaker shipped the painting to Boston's Museum of Fine Arts for safekeeping. In 1962, it was bought by US collector Henry Pulitzer. When he died in 1979, his reported mistress - Elisabeth Meyer - inherited it, but it remained in a Swiss bank vault. After she died, an "international consortium" bought the painting in 2008. The foundation was set up two years later, determined to try to show that it was a real da Vinci.