A charcoal drawing attributed at least in part to Leonardo da Vinci, known as the Monna Vanna, may be a nude sketch of Mona Lisa, the Guardian is reporting.

“The drawing has a quality in the way the face and hands are rendered that is truly remarkable. It is not a pale copy,” curator Mathieu Deldicque told the outlet. “We are looking at something which was worked on in parallel with the Mona Lisa at the end of Leonardo’s life. It is almost certainly a preparatory work for an oil painting.”

Leonardo da Vinci and workshop. Monna Vanna, c.1515. Musée Condé – Chateau de Chantilly. Enjoy the details: https://t.co/byKEUxobpo pic.twitter.com/P4dO5UMmNA — ColecciónMMoret (@ColeccionMMoret) September 29, 2017

The drawing is reportedly almost exactly the size of the Mona Lisa, and a conservation expert at the Louvre confirmed that the piece of art was created at the turn of the 15th century when da Vinci was still alive. Now, experts are working to identify whether or not the sketch was done before or after the Mona Lisa. She was painted sometime after 1503.