A portrait of Pablo Picasso's lover Marie-Therese Walter sold in London on Tuesday night for £28.6 million (RM138.34 million), Southeby's auction house said.

The colourful and curvaceous "Femme assise pres d'une fenetre" (Woman sitting by a window), painted in 1932, was sold at a crowded salesroom to an anonymous telephone buyer, a Sotheby's spokesman said.

It had been expected to go under the hammer for between £25 million (RM120.93 million) and £35 million (RM169.30 million).

"We are delighted that this stunning and monumental portrait, which is part of the defining series that introduced his 'golden muse' to the public eye, fetched such a strong price," said Helena Newman, chairwoman of Sotheby's impressionist and modern art department in Europe.

"This particular portrait is a striking and notably modern-looking work from one of the artist's most celebrated periods."

The painting was the star lot in Tuesday's impressionist, modern and surrealist art sale, achieving the top price in an auction that netted a total of £121 million (RM585.30 million).

Picasso met his famous muse Marie-Therese Walter in Paris in 1927, when she was 17 and he was 45. Their relationship was kept secret for many years because of her youth and Picasso's marriage to the Russian ballerina Olga Khokhlova.

The affair was revealed in 1932 when portraits of Walter were displayed for the first time alongside other Picasso works in a major retrospective, and Khokhlova realised there was another woman in her husband's life.

Walter, who inspired several of Picasso's works including "La Lecture", "La Reve" and "Nature morte aux tulipes", bore the Spanish artist a daughter, Maya.

"In recent years in particular we have witnessed the remarkable allure of Picasso's portraits of Marie-Therese to collectors," Newman said.

Another portrait of Walter from the same series, "Nude, Green Leaves and Bust", held the record for the most expensive work of art ever sold at auction when it was bought for $106.4 million (RM328.62 million) in New York in 2010.

It was ousted last May when "The Scream" by Edvard Munch sold for $119.9 million (RM370.31 million).

"La Lecture" sold at Sotheby's in 2011 for £25 million (RM120.93 million), double its pre-sale estimate, while "Nature morte aux tulipes" went under the hammer in New York last November for $41.5 million (RM128.17 million).

Also sold on Tuesday was Claude Monet's lily painting "Nympheas avec reflets de hautes herbes", which went for £9.0 million (RM43.53 million).

A piece by Egon Schiele, Liebespaar, also netted a record price for a work on paper by the Austrian artist, at £7.9 million (RM38.21 million).