A lost masterpiece hidden away in the attic of a French chateau for 200 years because its owners thought it was too racy, could fetch up to £900,000 when it is auctioned tomorrow.



The painting of a voluptuous and partly-clad young woman is by Giambattista Tiepolo, one of the most brilliant and sought-after Italian painters of his time.



Earlier this year, the grandchildren of the original owners brought it down from the dust and gloom to see the light of day for the first time since the 19th century.



The 35in by 27.5in oil - entitled Portrait Of A Lady As Flora (the classical Goddess of Spring) - is estimated to make £700,000 to £900,000 at Christie's Important Old Masters evening sale.



Richard Knight, international director of Christie's Old Master Department, described it as 'one of the most exciting and extraordinary discoveries of recent years'.



He confirmed it had been found in the the attic of a French chateau 'where it had been hidden by the grandparents of the present owners due to the semi-naked subject'.



He added: 'The painting has lain untouched in the same private collection for over 200 years, and as a result it remains breathtakingly similar to the way it would have been immediately after it left the artist's easel.

'Private collectors are attracted to rare, rediscovered paintings offered in untouched condition.'



The painting of the enigmatic, fleshy young woman, left breast provocatively exposed, is previously unpublished and is probably from a series of pictures commissioned some time just before 1760 by Empress Elizabeth of Russia (1709-1762).



It has never before been seen in public and had remained in the family chateau of the present owners since 'at least' the 19th century.



The painting is undated but thought to be undertaken in the 1750s and there is considerable debate about the identity of the model.



One theory is that she is a gondolier's daughter called Christina.



According to art historians, Tiepolo valued her so highly as a model that when he and his family moved to Spain in 1762, he brought Christina too so he could keep painting the woman who was 'beautiful with a haughty look'.



Another theory is that the model is Tiepolo's wife, Cecilia Guardi, sister of the painter Francesco Guardi.



Giambattista (or Giovanni Battista) Tiepolo was born in Venice in 1696 and was at his peak in the 1750s and 60s.



He was called to Madrid to paint for Charles III of Spain and spent the last eight years of his life there, dying in 1770. He is said to have inspired Goya.