A nearly 500-year-old painting attributed to Leonardo da Vinci that was believed to have been lost for centuries was discovered in a Swiss bank vault on Friday.

According to the Telegraph, experts think the painting is a completed, painted version of a pencil sketch da Vinci did in 1499. His subject was Isabella d’Este, Marchesa of Mantua, a prominent Italian noblewoman and a muse of the artist. According to the Brooklyn Museum, d’Este became the acting regent of Mantua in 1509 when her husband, the fourth marquis of the city, was taken as a prisoner of war. She went on to become an immensely popular political figure and later become a big patron of the arts.

The sketch, done in Italy’s Lombard region in 1499, is currently on display at the Louvre in Paris. But, like da Vinici’s “Battle of Anghiari,” a completed version of the piece has eluded experts for centuries.

However, Carlo Pedretti, a University of California at Los Angeles professor emeritus of art history who specializes in da Vinci, believes a collection of hundreds of pieces stored in a Swiss vault contains what is likely an original by the Italian master, Italy’s Corrierre Della Serra reported.

“There are no doubts that the portrait is the work of Leonardo,” Pedretti said, adding that scientific tests appeared to authenticate the work. “I can immediately recognise Da Vinci’s handiwork, particularly in the woman’s face.”

Pedretti said further investigation is needed to determine how much of the painting was done by da Vinci, and how much by his apprentices.

But not everyone is convinced the find is an authentic piece of da Vinci artwork. Martin Kemp, a professor emeritus of art history at Trinity College at Oxford, told the Telegraph he was skeptical about the piece’s authenticity because it was painted on canvas and da Vinci preferred to work with wood. “You can’t rule out the possibility, but it seems unlikely,” he said.