Mrs Baldwin was British, but born in Turkey. She travelled widely.

The 1782 painting reached its estimate price of between �3m and �4m at the sale in London on Thursday.

The portrait of a merchant's wife called Mrs Baldwin was sold to the Compton Verney gallery in Warwickshire.

A similar painting of Mrs Baldwin was withdrawn from a Christie's auction in 2003 when it emerged it was mainly painted by Reynolds' studio assistants.

"We were delighted to see Reynolds' dazzling portrait of Mrs Baldwin achieve such a good price," said David Moore-Gwyn, head of British paintings at Sotheby's.

Attractive

"We were especially pleased to see it go to such a good home: the fact that it was bought for the Compton Verney Art Gallery means that those visiting the gallery will now have the opportunity to enjoy one of Reynolds' finest works," he added.

Mrs Baldwin, a merchant's wife, attracted many admirers including Emperor Joseph and Doctor Johnson.

When she visited Vienna in 1780, Emperor Joseph was so entranced with her beauty he commissioned a portrait bust of her.

Reynolds' painting was not a commissioned work - it was something he painted on his own initiative.

Record

Unusually, the artist was so proud of his painting of Mrs Baldwin that he kept the portrait and it was only sold after his death in 1792.

The auction record for a painting by Reynolds was set in November 2001, when Sotheby's sold Portrait of Omai for �10,343,500.

In June last year, Sotheby's sold Reynolds' Portrait of Lady Kent for �2,690,600 - the second highest auction price ever reached for a work by the artist until Portrait of Mrs Baldwin was sold.

It went for five times the reserve price.