PARIS (REUTERS).- A sensual 1932 portrait by Pablo Picasso of his young mistress Marie-Therese Walter which captures his romantic obsession with her went on display at Sotheby's in Paris on Wednesday ahead of an auction next month.

It was the first public showing in Europe in some 80 years of "La Lecture," or "Reading," an erotic and brightly colored depiction of the voluptuous Marie-Therese sleeping nude in an armchair, her head thrown back and an open book in her lap.

Painted in bright yellow, green and red oils at the height of what art experts call Picasso's "lovestruck" period, it will be the star offering at an upcoming sale of Impressionist and Modern art by Sotheby's in London.

Experts say the painting could fetch between 12 and 18 million pounds ($19 to $29 million) after another 1932 Picasso portrait of Marie-Therese, "Nude, Green Leaves and Bust," was sold by rival auction house Christie's in New York for $106 million in 2010 -- an all time record for an art auction.

"In the early 1930s he was very lyrically in love and reflected that in these gorgeous colors, and lovely compositions," Philip Hook, Director of the Impressionist and Modern Picture Department at Sotheby's in London told Reuters.

"This period is just about the most desirable of all Picasso's (periods), certainly in market terms," he said.

Marie-Therese was one of a series of lovers and muses who inspired Picasso throughout his prolific eight-decade career.

She first caught his eye in 1927, aged just 17, as she was coming out of the Paris Metro on her way back from a shopping trip. Picasso, in his mid-forties, was immediately smitten.

Marie-Therese later said he took her by the arm and said: "I am Picasso. You and I are going to do great things together."

Although still married to his first wife, Russian dancer Olga Khokhlova, Picasso began a covert affair with Marie-Therese, who later gave birth to their daughter, Maya or Maria de la Concepcion.

(Reporting by Vicky Buffery; Editing by Catherine Bremer and Paul Casciato)