An Andy Warhol self-portrait, one of the last to be completed before his death, is expected to sell for as much as US$40 million at a Christie's auction next month. 'Self-Portrait', a large, brooding depiction of the artist rendered in vermilion and black, was done in 1986 and displayed in a widely acclaimed gallery show in London, just months before he died from complications after a routine surgical procedure in New York. 'It is a rare event that a work of this grandeur and stature comes to market,' said Amy Cappellazzo, Christie's international co-head and deputy chairman of post-war and contemporary art. 'With all the other examples in museums, it will be the last chance that buyers will have to bid on a work that shifted art history.' The auction is slated for May 11.