Portrait of Jeffrey Bernard's brother to set Freud record

It is an intimate portrait of a close friend, with his hands stuffed in his pockets and a visible tension etched on his face. Lucien Freud's painting of Bruce Bernard, the brother of the legendary bon viveur Jeffrey Bernard, and part of his "Soho circle" of artists and writers, is expected to fetch a record £5.5m at auction on 20 June.

Bernard, who died in 2000, worked as a journalist and was a former art director ofThe Independent. He was a friend to Freud for many years and edited a series of books and monographs on the artist.

The two men met on the Soho scene and Bernard began socialising with the key affiliates of the "School of London" artists, a circle which included Frank Auerbach and Francis Bacon.

The pair would drink regularly in Soho, along with Jeffrey Bernard, who was immortalised in Keith Waterhouse's play Jeffrey Bernard is Unwell.

The work, painted in 1992, captures the casual intimacy between them, showing Bernard standing on the floorboards of Freud's studio in Holland Park, west London, with white rags that were used by the painter to clean his brushes, piled in a corner. It is believed to be the most important painting by Freud ever to appear at auction.

In all, Bernard sat for two portraits and an etching. A painting of him seated with his fists on his thighs sold for £3.5m last year to the New York-based private dealer Christopher Eykyn.

Pilar Ordovas, the head of post-war and contemporary art at Christie's, which will auction the work, said the painting perfectly captured the fondness between the two men. "It's so important because he [Bernard] was so close and personal to the artist, and it is a powerful and highly successful portrait for that reason. It is psychological in the sense that Freud captures the amazing tension in the face," she said.

The portrait, which features in a sale of post-war and contemporary art, is owned by the New York collectors Elaine and Melvin Merians. Its estimated price is likely to exceed the current record for a Freud painting, sold in 2005, which stands at £4.2m for Red Haired Man on a Chair.

Born in Berlin in 1922, Freud is the grandson of Sigmund Freud, the founder of psychoanalysis. He served in the Royal Navy during the Second World War.

He had set the record for being Europe's most expensive living artist, until Peter Doig, a relatively unknown British painter, overtook him in February when hisWhite Canoe fetched £5.7m. But prices for Freud's art have rocketed in the past decade and the sale of Bruce Bernard could mean that he reclaims his title.

The painting is among 21 major works by the School of London artists up for auction on 20 June. They include Francis Bacon's Two Men Working in a Field, completed in 1971 and expected to fetch up to £7m, and Frank Auerbach's Tree in Mornington Crescent, from 1991, which is expected to sell for £1.5m. Pieces by Paula Rego and RB Kitaj will also be sold.