A U.S. gallery spent 2.95 million pounds ($4.6 million) at auction here Wednesday to acquire a rediscovered painting attributed to Spanish master Diego Velazquez (1599-1660).

The buyer was Alfred Bader Fine Arts of Milwaukee, whose vice president, David Bader, was present at the bidding at Bonhams in London, though the actual bidding was handled by his partner Otto Naumann, who said it was the "bargain of the decade."

Naumann admitted being "astonished" at having managed to acquire the small canvas piece at "such a low" price.

The New York agent said that the price for the portrait, which Bonhams had valued at between 2 and 3 million pounds, could have been "6 or 7 million pounds" ($9.4-$10.9 million).

The painting, which was sold without a frame, is of the bust of a bald middle-aged man, dressed in black and wearing a stiff white collar.

The work, part of a collection of 63 works by old masters, has been surrounded by questions regarding who painted it.

The find of this unexpected portrait by Velazquez was made public in the latest issue of Ars Magazine in an article by Peter Cherry, a lecturer in art history at Trinity College Dublin.

The painting originally was to have been auctioned in August 2010 by Bonhams in Oxford, England, as part of a batch of paintings by 19th century British artist Matthew Shepperson.

However, Bonhams curators noticed the similarity of the piece with Velazquez's style and separated it from the other works to investigate it further.

More than a year later, during which time Bonhams undertook technical analyses on the work, the auction house's experts determined and certified that the Spaniard was its creator.

The director of old master paintings at Bonhams, Andrew McKenzie, acknowledged Wednesday that those doubts about the authorship of the work could have influenced its price.

Regarding the piece, Velazquez specialist Benito Navarrete said Wednesday in Spain that it is a "work by the hand of Velazquez and should be in the Prado Museum."