A newly discovered statue of St George by the major 19th and early 20th century British sculptor, and creator of Eros at Piccadilly Circus, Sir Alfred Gilbert, is to be offered at Bonhams' Fine Design 1200-1900 sale in London on Wednesday 18 December. A close variant on Gilbert's design for the statue of St George on the tomb of the Duke of Clarence in St George's chapel, the piece is believed to be unique. It is estimated at £80,000-120,000.

In 1892, Prince Albert Victor, Duke of Clarence – the eldest grandson of Queen Victoria, and hence second in line to the British throne – caught flu and died. His grief-stricken parents, the future King Edward VII and Queen Consort Alexandra, commissioned Sir Alfred Gilbert to design bronze statues of saints to adorn his tomb in St George's Chapel, Windsor. The figures – of which, St George, England's patron saint, was the best known – were installed in 1895.

Gilbert, the premier English sculptor of the day controversially capitalised on the appeal of St George by accepting commissions to make copies for private clients. A very small number of these, in a variety of media and, at 50cm, the same size as the original, have survived. The bronze statue in the sale, however, is, at 90cms high, considerably larger. It was discovered by Bonhams specialists during a country house valuation. After extensive research, Bonhams Head of European Sculpture and Works of Art, Michael Lake, has identified the work as a commission from John Charles (J.C.) Williams of Werrington Park, Launceston. Liberal Unionist MP for Truro in the early 1890s and a noted botanist, Williams ordered St George in 1895. It was apparently the first part of a commission for four double size figure replicas, but the other three representing the patron saints of Ireland, Scotland and Wales were apparently never realised.

Michael Lake said, "This is a tremendously exciting discovery and appears to be unique. We know that Mr Williams stipulated that no copies should be made and although Gilbert was notorious for ignoring his clients' instructions in that regard, it seems that in this instance, he did actually destroy the mould. It is a major piece by one of Britain's best loved and finest sculptors and I think will have great appeal to collectors, both private and public."

Art critic and historian Richard Dorment, an authority on Gilbert who curated the Alfred Gilbert: Sculptor and Goldsmith exhibition at the Royal Academy of Arts in 1986 said: "This is an extraordinary statue and that rare thing, a fully documented Gilbert cast from the 1890s."