AFP - A portrait of William Shakespeare believed to be the only surviving picture of the British playwright painted during his lifetime was unveiled in London on Monday.

The painting, which dates from 1610 — when the Bard was 46, six years before his death — has been owned by the same family for centuries but was only recently identified.

Art restorer Alec Cobbe said his family took possession of it when a cousin married the great granddaughter of Shakespeare's only literary patron, Henry Wriothesley, the third Earl of Southampton.

Three years ago Cobbe noticed the similarity of the painting to one displayed at the National Portrait Gallery, and it was subsequently identified by experts as the only portrait painted before the playwright died.

"The identification of this portrait marks a major development in the history of Shakespearean portraiture... This new portrait is a very fine painting," said Professor Stanley Wells of the Shakespeare Birthplace Trust.

The portrait will go on display at the Shakespeare Birthplace Trust in the Bard's home town of Stratford-upon-Avon in an exhibition opening on April 23, his birthday.