A newly discovered portrait by the famed 17th century Spanish painter Diego Velazquez sold at Bonhams in London yesterday for £3 million, or $4.7 million. The sum represented nearly half of the earnings at Bonhams’ Old Master Paintings sale. The painting was brought to Bonhams’ Oxford location in 2010 as part of a group of paintings by the 19th century British artist Matthew Shepperson. Questions about the painting’s attribution led to an investigation of the portrait by both in-house and outside experts. The Velazquez attribution was aided by the use of x-ray technology. The painting is one of only about 100 works by the artist known to exist, very few of which are in private hands. The painting sold for $4.7 million, reportedly to an American buyer.