London: The world's most famous painting Mona Lisa may not be unique after all, as experts claim that an earlier version, unearthed last year, is also the work of Leonardo da Vinci.
The so-called Isleworth Mona Lisa, which shows a significantly younger subject, may be several years older than its more famous counterpart, the Daily Mail reported.
The Mona Lisa, which has been on display in the Louvre in Paris for three centuries, has long been regarded as the only one painted by the Italian master.
But recent tests have shown that the other portrait is almost certainly da Vinci's work, according to a Swiss-based art foundation.
The Isleworth Mona Lisa, once belonged to a Jane Blaker, who lived with the art-collecting Davies sisters in Powys.
It was bought by Blaker's brother Hugh in 1913, who is best known as a picture advisor to the sisters.
Blaker was from Isleworth, West London - hence the name.
Carbon dating placed its creation in the correct era, refuting claims that it was a later copy of the main painting, which was created in around 1516.
Analysis by a specialist in geometry has shown it matches the proportions da Vinci depicted in his human forms.
The results may help convince experts who were sceptical when the painting was unveiled in Geneva last year, after it had been kept in a Swiss bank vault for four decades.
The international group, which says it has no financial interest in the work, claimed today that its authenticity has finally been proven.