The auction house thought the tiny portrait was a 17th century Rembrandt knockoff, and valued it at just 1,500 pounds (US$3,100). But the British buyer who paid about 1,500 times that apparently knew what he was doing. Experts have confirmed "Rembrandt Laughing" - bought for a bargain price of 2.2 million pounds (US$4.5 million) at an English auction house in October - is in fact a self-portrait by the 17th-Century Dutch master himself, depicted with his head tilted back in easygoing laughter. "That picture's clearly worth between 15 and 20 million pounds," or US$30 million to US$40 million, said William Noortman from Noortman Master Paintings, specializing in Dutch and Flemish masters. "I'm very surprised it didn't make more at auction," he said Wednesday. The 24.1-by-16.5-centimeter painting now hangs in the Rembrandt House Museum in Amsterdam through June 29, on loan from the anonymous Briton who bought it at the auction by Moore, Allen and Innocent in Gloucestershire and had it cleaned and examined by British experts.