A painting from the Claude Monet waterlily series which has not been seen in public for 77 years has sold for more than �13m ($20m) at auction.

It became the most expensive painting to be sold in London this year when it went under the hammer at Sotheby's.

Nympheas, which Monet painted in 1906 as part of his famous waterlilies series, went to an anonymous bidder for �13,481,650.

The Impressionist masterpiece was last shown in public in 1925.

The present owner's grandfather bought it in 1940 and it has remained in the family's private collection in rural France ever since.

It had been expected to fetch between �10m and �15m and a Sotheby's spokeswoman said they were "delighted" with the sale.

The record for a Monet was set in 1998 when one of his paintings sold for �19.8m at Sotheby's.

The sale also contained works from Pablo Picasso, Vincent van Gogh, Edgar Degas, Paul Cezanne and Edvard Munch.

Famous pond

"It is in a pristine state, unvarnished and unlined," said a Sotheby's spokesman.

"To stand in front of it today is to see it in much the same condition as it was when it left Monet's studio."

Monet created the famous waterlily pond in his garden at Giverny, where he moved in 1883, and it inspired much of the remainder of his work.

Experts were worried that the recent economic downturn in the US would affect art prices, but the spring auctions have seen record prices for many "blockbuster" items.

The most recent auction of a major Monet work saw Haystacks: Last Rays of the Sun sell for �10m at Sotheby's in London after a three-way bidding war.

Weather conditions

Monet is often described as a painter who intently studied the fleeting effects of light on the natural world.

Born in Paris on 14 November 1840, he spent most of his childhood in Le Havre, northern France.

It was a feature of his work that he would paint a particular subject in a variety of weather conditions or times of day or year.

Monet's painting Impression, Sunrise also gave the Impressionists their name and earned Monet his "father of the impressionists" title.