Warhol's final self-portraits reveal his darker side

Six months before Andy Warhol died of a heart attack, he finished painting his last series of self-portraits. They differed dramatically from anything he had previously produced.

The artist and founding father of Pop Art had spent a lifetime "playing" with his own image in ways which left his emotions illusive. But these final portraits, created in 1986, were far darker and more revelatory, exposing a paralysing fear of death in a set of paintings which showed his stark, skull-like face staring out of the canvas.

In the images, set on an inky black background, his bald head is covered by his famously disconcerting "fright wig".

The works, which have not been seen for more than two decades, will be unveiled at Sotheby's in New York today. When they are sold next month in London, it will be the first time they have appeared on the market since his death. They are expected to sell for more than £10m.

Warhol's final series of self-portraits is now widely accepted as the most important of his career. It reflects the phobia of doctors he developed at a time when he was suffering from recurring gall bladder problems, but delayed treatment and grew increasingly afraid of hospitals.

Warhol died the night after he brokered their sale to a private collector. Since his death, on 22 February 1987, the images have come to represent his fear of his own mortality and descent into paranoia.

Created for the only dedicated exhibition of self-portraits to be staged in his lifetime, the trinity of red, white and blue silk screens represent the colours of the American flag.

The three 40-inch canvases are the only ones in theoriginal series of six works to remain together. The other three, pink, green and yellow, versions are held in separate private collections worldwide.

This series is universally acknowledged as Warhol's last great artistic gesture in which he returned to the form he had reached at his creative height in the 1960s, when he was also producing his silk-screen prints of Hollywood celebrities including Marilyn Monroe, Elizabeth Taylor and Elvis Presley.

Francis Outred, head of evening auctions at Sotheby's, said the silk screens were bought by the present owner from the artist's exhibition at Anthony d'Offay's gallery in London, which displayed portraits bought by the Tate gallery in London, the Metropolitan Museum of Art in New York and the Carnegie Museum in Warhol's home town of Pittsburgh.

Mr Outred said that although he was deeply self-conscious about his personal appearance, which became more fragile and eccentric as he aged, Warhol reproduced his own image prolifically.

He used different guises throughout his career, sometimes half-hidden by shadows, sunglasses or a mackintosh, and at other times in drag or dressed as a streetwise New Yorker sitting in a photo-booth, but always presenting himself as a distant, machine-like recorder.

In these late examples, Warhol appears to be reaching the end of his apparent endeavour to present himself as a "consumer brand", now perhaps past its prime.

"Throughout his career he became known for his pop art and portraits of celebrity icons, as if he recognised the society we live in even before we did," Mr Outred said.

"What's important about his self-portraits is that it marked the rise of his own brand, that itself became iconic. Why these are so important is that he was coming to the end of his life and although he did not know this, he was certainly thinking of his life, mortality and posterity."

He continued: "What also differs is that before he never appeared to fully reveal himself in his self-portraits, but here he has piercing eyes and paints himself with his fright wig, which he wore because he was losing his hair.

"It's as if this time he wanted to show himself exactly as he was."