A portrait of Pablo Picasso’s lover Marie-Therese Walter sold in London on Tuesday night for £28.6 million ($45.0 million), Sotheby’s auction house said.

The colourful and curvaceous “Femme assise pres d’une fenetre” (Woman sitting by a window), painted in 1932, was sold to an anonymous telephone buyer.

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.

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.

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 in New York in 2010.