LONDON (REUTERS).- A Rembrandt painting unseen in public for nearly 40 years sold for a record 20.2 million pounds ($33.2 million) at auction in London on Tuesday, the highest ever paid at auction for the 17th century artist.

Christie's said that "Portrait of a man, half-length, with his arms akimbo", painted in 1658, fetched the 4th highest-price paid at auction for any old masters painting.

It was bought by an anonymous client bidding via telephone, Christie's said.

The record for a Rembrandt previously stood at 19.8 million pounds (then $29 million) in December 2000 for "Portrait of a lady aged 62."

The Rembrandt was the star lot in Christie's auction of old masters and 19th century works, which have stood up relatively well during a financial downturn that has hit much of the rest of the world art market.

"We are delighted to have been able to exhibit this masterful portrait for the first time in nearly forty years leading up to the auction, and to have seen it realize such a strong price that reflects its importance and magnitude," said Richard Knight, international co-head of old masters at Christie's.

The last time the 1658 Rembrandt painting was sold at auction was in 1930 when it fetched 18,500 pounds. It later went into a series of private collections in the United States and was last seen in public at an exhibition in Detroit in 1970.

The top price at auction for any old master picture is 49.5 million pounds ($77 million) for "The Massacre of the Innocents" by Peter Paul Rubens set at Sotheby's in London in 2002.

(Editing by Bob Tourtellotte)