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Leonardo da Vinci painted a younger and happier Mona Lisa some 10 years before painting the famous painting, art experts are claiming.

Slightly larger in size than the famous portrait,‭ ‬which now hangs in the Louvre in Paris,‭ ‬the painting features‭ ‬a darker tonality,‭ ‬a different and unfinished background framed by two columns,‭ ‬and‭ ‬shows a younger lady with a less enigmatic smile.

Known as the Isleworth Mona Lisa,‭ ‬the artwork will be unveiled in Geneva on Thursday by the Mona Lisa Foundation,‭ ‬a Zurich‭-based consortium which has‭ ‬kept the painting in a Swiss bank vault for‭ ‬40‭ ‬years.

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A‭ ‬320-page book will provide‭ "‬historical,‭ ‬comparative and scientific evidence‭" ‬to prove once and for all that the‭ ‬Isleworth work is an authentic Da Vinci artwork,‭ ‬a spokeman of the Swiss foundation said.

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Leading‭ ‬Da Vinci experts Alessandro Vezzosi,‭ ‬the director of the‭ ‬Museo Ideale in the Tuscan town of Vinci,‭ ‬where Leonardo was born in‭ ‬1452,‭ ‬and Carlo Pedretti of the Armand Hammer Center for Leonardo Studies at the University of California,‭ ‬will‭ ‬discuss the claim.

They have made no attribution to Da Vinci,‭ ‬as they believe further study is needed.

Indeed,‭ ‬the painting's authenticity has been the subject of debate ever since the canvas was discovered‭ ‬in‭ ‬1913‭ ‬by English art collector Hugh Blaker.

He bought it from a noble family‭ ‬and took it to his studio in Isleworth,‭ ‬London‭ – ‬hence the name.

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In‭ ‬1915‭ ‬his stepfather‭ ‬John R.‭ ‬Eyre,‭ ‬an art historian,‭ ‬published‭ ‬a book‭ ‬suggesting that Leonardo painted two versions of‭ the ‬Mona Lisa‭ ‬and claiming that‭ ‬at least the bust,‭ ‬the face and the hands of the‭ ‬Isleworth lady‭ ‬were a genuine work by‭ ‬Leonardo Da Vinci‭ –- ‬basically,‭ ‬a‭ ‬prequel to his famous portrait.

Blaker then sold the painting‭ ‬to American collector Henry F. Pulitzer,‭ ‬who in turn left it to his girlfriend. On her death,‭ ‬it was bought by the Mona Lisa Foundation, a consortium of unnamed individuals.

Pulitzer carried out more in depth research on the painting and reinforced Eyre's theory in his‭ ‬1966‭ ‬book,‭ "Where is the Mona Lisa‭?‬"

He looked into the accounts of the‭ ‬16th century painter and art historian Giorgio Vasari.

In his work‭ "‬Lives of the Artists,‭"‬ Vasari (1511–1574) named Lisa Gherardini,‭ ‬the wife of the wealthy Florentine silk merchant Francesco del Giocondo as the subject of the portrait and concluded that the‭ ‬work‭ ‬was painted‭ ‬by Leonardo‭ ‬between‭ ‬1503‭ ‬and‭ ‬1506.

‭ ‬"Toiling on it for four years,‭ ‬he left it unfinished,‭" ‬Vasari wrote.

As‭ ‬Da Vinci sold a fully finished Mona Lisa to King Francis I in‭ ‬1516‭, three years before his death, ‭‬supporters of the‭ ‬Isleworth work argue that the painting‭ ‬is‭ ‬ the unfinished‭ ‬Mona Lisa,‭ ‬partially made‭ ‬by Leonardo and originally handed over to‭ ‬the‭ ‬patron who had commissioned it.‭ ‬The Louvre masterpiece‭ ‬would then be a later version,‭ ‬made by Da Vinci for his own‭ ‬use.

To support the theory,‭ ‬Pulitzer‭ ‬references‭ ‬Giovanni Lomazzo,‭ ‬a biographer of artists,‭ ‬who in his‭ ‬1584‭ ‬Treatise on Painting referred to "the Gioconda,‭ ‬and the Mona Lisa‭."‬

Since‭ ‬La Gioconda is‭ ‬the Italian alternative name for the‭ ‬Mona Lisa hanging in the Louvre,‭ ‬Lomazzo's reference would imply that there were two‭‭ ‬distinct and separate‭ ‬paintings.‭

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Pulitzer also focused on the columns which frame the‭ ‬Isleworth lady.‭ ‬Similar columns‭ ‬are also shown in a drawing by Raphael of the Mona Lisa.‭ ‬Now in the Louvre,‭ ‬the drawing was probably done from memory from Leonardo's original after Raphael visited the master studio in‭ ‬1504.

Moreover,‭ ‬Vasari's description of the Mona Lisa portrait as having‭ "a smile so pleasing‭" ‬was‭ ‬often‭ ‬quoted against the Louvre picture,‭ ‬of which the effect has been variously described as enigmatic,‭ ‬mysterious and baffling.

The Isleworth picture has a real smile,‭ ‬it was‭ ‬argued.‭

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But doubts about Vasari's attribution have persisted since he was known to rely on anecdotal evidence.‭ ‬The authenticity of the‭ ‬Isleworth Mona Lisa remained widey disputed among art historians. ‭

"‬So much is wrong.‭ ‬The dress,‭ ‬the hair and background landscape.‭ ‬This one is also painted on canvas,‭ ‬which Leonardo rarely did,‭" ‬Martin Kemp,‭ ‬emeritus professor of the history of art at Oxford,‭ ‬told The Sunday Times.

Like the majority of‭ ‬Leonardo's works,‭ ‬the Mona Lisa in the Louvre is‭ ‬painted on wood. ‭

"‬She might look younger but this is probably because the copyist,‭ ‬and I believe it is a copy done a few years after the Mona Lisa,‭ ‬just painted it that way,‭" ‬Kemp said.