A recently attributed painting by 17th century Spanish artist Diego Velazquez sold at auction in London on Wednesday for £3 million ($4.7 million, 3.5 million euros), Bonhams auction house announced. "Portrait of a Gentleman" -- a painting of a bald, middle-aged man with a moustache wearing a collar similar to those worn by men in the 1600s -- was bought by a US art dealer for a price within the auction house's estimate. The painting was first spotted in August 2010 among a number of works by 19th century British artist Matthew Shepperson which had been brought to Bonhams' office in Oxford for sale. After extensive research by the auction house and tests including an x-radiograph, the painting was identified as a Velazquez and confirmed by Doctor Peter Cherry, an expert on the Spanish artist at the University of Dublin. "Velazquez is one of the greatest geniuses in the entire history of Western art. The discovery of this lost treasure is a once in a lifetime experience," said Andrew McKenzie, director of Old Master Paintings at Bonhams.