An image of a portrait underneath the Mona Lisa has been found beneath the existing painting using reflective light technology, according to a French scientist.
Pascal Cotte said he has spent more than 10 years using the technology to analyse the painting.
He claims the earlier portrait lies hidden underneath the surface of Leonardo's most celebrated artwork.
A reconstruction shows another image of a sitter looking off to the side.
The Louvre Museum has declined to comment on his claims.
Instead of the famous, direct gaze of the painting which hangs in the Louvre Museum in Paris, the image of the sitter also shows no trace of her enigmatic smile, which has intrigued art lovers for more than 500 years.
But Mr Cotte's claims are controversial and have divided opinion among Leonardo experts.
The scientist, who is the co-founder of Lumiere Technology in Paris, was given access to the painting in 2004 by the Louvre.
He has pioneered a technique called Layer Amplification Method (LAM), which he used to analyse the Mona Lisa.
It works by "projecting a series of intense lights" on to the painting, Mr Cotte said. A camera then takes measurements of the lights' reflections and from those measurements, Mr Cotte said he is able to reconstruct what has happened between the layers of the paint.
The Mona Lisa has been the subject of several scientific examinations over more than half a century. More recent techniques include infrared inspections and multi-spectral scanning.
But Mr Cotte has claimed his technique is able to penetrate more deeply into the painting.
He said: "We can now analyse exactly what is happening inside the layers of the paint and we can peel like an onion all the layers of the painting. We can reconstruct all the chronology of the creation of the painting".