Claude Monet's masterpiece Nympheas has been sold at auction for £18.5m at Sotheby's in London.
The painting, which had been expected to sell for £15m, was seen as one of the finest of Monet's water lily series to have come on to the market.
But, despite expectations, it failed to break the artist's auction record of £19.8m, set in 1998.
A view of the River Thames by Monet sold for almost £18m - more than twice its estimate - at Christie's on Monday.
His paintings of water lilies are among the most iconic images of Impressionism, and only a few such works remain in private hands.
Painted in Monet's garden at Giverny in 1904, Nympheas was bought from Michel Monet, the artist's son, in the 1920s by a French collector, and remained in the same family for 80 years.
The masterpiece, which had not been seen in public since 1936, was bought by an anonymous American bidder over the phone.
Art expert Bobby Read said the sale showed there was currently a "buzz" in the London art scene.
Matisse's Danseuse Dans Le Fauteuil set a sales record
"It is unsurprising that this piece by Monet sold at such a high price. It is an exceptional example of his water lily series which is one of the most iconic images of impressionism.
"Our figures show that modern art has rocketed in value in the last year."
The auction also featured works by Pablo Picasso, Amedeo Modigliani and Pierre-Auguste Renoir.
A painting by Henri Matisse set a new auction record for the artist.
Danseuse Dans Le Fauteuil, Sol En Damier sold for £11m, towards the higher end of its pre-sale estimate of £8-12m.
On 21 June, Sotheby's is holding its biggest contemporary art sale, including a self-portrait by Francis Bacon, expected to fetch up to £12m, and several works by Andy Warhol.
Art experts estimate that this week's London sales could generate almost £500m.