A recently unearthed sketch of a nude woman, believed to have been drawn by Leonardo da Vinci, could be of the 'Mona Lisa' herself.
The sketch dates from the time and region of Italy where the master painter and inventor lived, but has spent the past 150 years in a collection in France.
The charcoal portrait is now undergoing forensic examination by experts to see if it's a genuine da Vinci, and a practise run at what would go on to become perhaps the world's most famous painting.
"The drawing has a quality in the way the face and hands are rendered that is truly remarkable," curator Mathieu Deldicque told AFP.
"It is not a pale copy. 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."
Mr Deldicque says the hands and body are "almost identical" and the portraits are the same size.
The biggest clue it might not be a da Vinci original is a hatching near the top right of the portrait - it's drawn by someone using their right hand, but da Vinci painted left-handed.