For sale: image of king's pet irritant

HE WAS known as the unofficial king of England; he was so powerful that his actions endangered relations between the English throne and Spain and France. George Villiers, first Duke of Buckingham, was the Court favourite of James I, and when James died in 1625 his successor, Charles I, adopted Buckingham's wife and children.

Now, a miniature of him by Jean Petitot, a Swiss enamellist, is to be sold for the first time - after it was discovered last year in London by Christie's, and is likely to realise between pounds 20,000 and pounds 30,000. The tiny portrait, in dazzling colours, was copied posthumously in 1640 from an earlier family painting of the maverick Duke and his family.

Born in 1592, the son of a Leicestershire knight, George Villiers won immediate favour at King James I's Court when he arrived in 1614. James showered him with money, land and titles, making him Marquis of Buckingham in 1618, Lord High Admiral of the Navy in 1619 and Duke of Buckingham in 1622.

In 1617, James said: "You can be sure that I love Buckingham more than anyone else. Christ had his John and I have my George." When the young Charles I ascended to the throne, Buckingham was so influential that he is thought to have made most of the king's important decisions for the next three years.

In spite of his legendary charm - he is regarded as one of the most charismatic figures in English history - he was ruthless in ensuring that no one rivalled him at Court. His interference in political affairs often had disastrous results, particularly the loss of good relations between England and Spain and France.

Even his old friend Sir John Coke called him "the cause of all our grievances". In 1628 he was assassinated with a single knife wound through the chest by Suffolk soldier John Felton, whom he had led on unsuccessful expeditions to Cadiz.

Alexandra Fennell, Christie's miniatures expert, is convinced that the miniature, to be sold on 30 April, is a remarkable find. He said: "There were only eight miniatures known by Jean Petitot before this work was found. He is the forefather of enamel painting. He came to London and worked at Court between 1637 and 1643 as servant to the Queen."

The Villiers miniature is part of a sale of important portraits at the King Street auction. There is also expected to be keen interest in portraits of Louis XVI in his coronation robes, Queen Elizabeth Christina of Prussia and Marie-Antoinette by her court artist Francois Dumont.

Other artists represented in the sale of miniatures from the 16th to 19th century include Samuel Cooper, Richard Cosway, John Smart, George Chinnery and William Wood.