Somewhere my love...Pasternak's passionate letters to his own Lara set to fetch pounds 500,000

Poignant exchange during Stalin purges

On screen and off, it was one of the most enduring love affairs of the 20th century. Those who saw the screen version will remember Omar Sharif and Julie Christie, as Dr Zhivago and the enigmatic Lara, in the Russian revolution epic.

But in real life, too, there was love and tragedy. For the character of Lara in Boris Pasternak's Nobel prize-winning masterpiece, Dr Zhivago, was based on his mistress, Olga Ivinskaya, the woman he loved until he died. in May, 1960.

The extent of their relationship, through Stalin's purges and despite periods of separation and imprisonment, has now come to light in a series of love letters, manuscripts and poems shortly to go on sale - at an estimated pounds 500,000 - at Christie's in London.

In them, Pasternak confirms that Olga was indeed the Lara of his novel, and he demonstrates his love for her throughout their hardships. The two spent much time apart, he in Tblisi, she in Leningrad, and his letters, discovered after Olga's death last year, often demonstrated a wish that they could be together.

"As always, I love you most deeply, but I'm sure you are neither aware of it, nor see any proof of it, and simply don't notice," he wrote in February, 1959.

"For my part, if I can hope that everything will remain as it was before our recent exchange of words, I would be in a state of perfect bliss. To imagine anything better than this would be inconceivable, beyond my power. I fancy I see something very, very good ahead of me, something undefinable and undeserved, a part of which I experience in advance as I embrace and kiss you in my thoughts."

Pasternak was awarded the Nobel prize for literature after his novel surfaced in Italy in 1957 - the book was not published in the Soviet Union - but he was forced to turn it down.

He was continuously harassed by the authorities and Olga herself was twice imprisoned in a gulag because of her relationship with him.

After rejecting the prize, he wrote that he had been "changed by the years of Stalin's atrocities, at which I gues-sed before they were exposed."

In his final letter, dated 5 May, 1960, he says he is convinced that he will recover, but goes on to describe pain so intense that he cannot shave.

"The razor falls from my hand from the stabs of pain in my shoulder-blade...," he wrote. However, he adds: "The factual evidence (the cardiogram and so forth) make it possible to believe that I shall recover. I already feel a little better."

Pasternak died of a severe heart attack, brought on by lung cancer, at 11.40pm on May 30, 1960.

Although Christie's admits that many of the letters and a collection of poems do not translate well, experts are nevertheless convinced that a figure of pounds 500,000 will be reached by the sale.

Peter Collingridge a specialist in books, manuscripts and Russian works of art at Christie's described the love letters as "absolutely beautiful."

They will go on sale on 27 November.