AN UNFINISHED portrait owned by the Bowood Estate is expected to fetch up to £3m when it is auctioned in London later this month.

The subject of the oil painting, by the artist Sir Joshua Reynolds is one of the 18th century's most talked about women Kitty Fisher.

It has been in the Lansdowne family for the past 150 years.

Produced in the 1760s, it was bought in May 1846 by the third Marquess of Lansdowne.

Lord Lansdowne, who lived between 1780 and 1863 formed a great library and art collection at Bowood and it is the trustees of this collection who have put the painting up for sale this month.

Kitty Fisher was immortalised in the nursery rhyme, Lucy Locket and Reynolds painted her portrait at least four times.

The Dictionary of National Biography states this prompted rumours they were lovers.

According to auctioneers Sotheby's who are dealing with the sale, Kitty was a beautiful object of fun and pleasure for men and that is how Reynolds portrays her.

She became one of the most celebrated figures in London and her beauty was legendary.

According to Horace Walpole she was recognised in a London park by both the young Prince Frederick William and his brother, the Prince of Wales (later King George III).

It is thought that she even caught the eye of the notorious womaniser Casanova, who was taken aback by her magnificence and charm.

She was said to have had liaisons with the minor politicians, lords, earls and other noblemen.

Only two were ever reported to have considered marrying her and both changed their minds.

Kitty died in 1767 aged 25 after only four months of marriage to Rye MP John Norris.

It is thought she died after using lead based cosmetics, although some say she died of smallpox and she asked to be buried in her favourite ball gown.

Sotheby's said of the portrait: "In this captivating and intimate portrait we are given a privileged glimpse of Kitty Fisher for which many men would pay vast sums of money.

"Painted in the most sensuous of lines, Kitty leans informally back in her chair.

"Her fur lined shawl and dress fall loosely covering and yet revealing her young form.

"This spontaneous unfinished portrait was painted by Reynolds in 1763- 1764.

"He was fast establishing his position as the most fashionable portrait painter of the day."

The painting will be auctioned on November 22.