But it's only now that scientists have spoken out about the chance that Leonardo's hand was behind both pieces of art. They pointed out that both the body of the women in the two pieces and her hands are remarkably similar.

They’ve also noted that the two pieces are very close in size, with the charcoal drawing featuring pierced holes suggesting it may have been used as a backdrop to trace a second image.

Bruno Mottin, a conservation expert at the Louvre museum, told Le Parisien newspaper that if nothing else, the Joconde Nue was an original from Leonardo's studio, and not one of the 20 or so copies of nude Mona Lisas around the world.

He added, however, that there were suggestions that others had worked on the piece too.

"The hatching on the top of the drawing near the head was done by a right-handed person. Leonardo drew with his left hand,” he told the French paper.

“It is a job that is going to take some time," he added.

"It is a very difficult drawing to work on because it is particularly fragile."

The month-long investigations into the drawing have seen scientists scanning the image in attempts to first determine if it was drawn before or after the Mona Lisa was painted, which was in 1503.