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Loved and lost: The portrait of Irish lawyer Thomas Lefroy, who married another woman but named his daughter Jane

A tiny portrait of the man a young Jane Austen loved and lost - believed to have inspired Pride And Prejudice's Mr Darcy - is to surface at an antiques fair.

The 3in watercolour of Irishman Thomas Langlois Lefroy was painted by leading English miniaturist George Engleheart in 1798, two years after the 20-year-old sweethearts were forced to part.

Lefroy's family, of Huguenot origin, was not wealthy and expected him to marry a woman of means.

But Austen, the sixth of seven children born to a Hampshire rector, was still 13 years away from her first literary success, Sense And Sensibility, and was not considered suitable marriage material.

The portrait on ivory - on the back of which are several locks of hair - was painted two years after Lefroy's dalliance with Austen.

It will be exhibited in London's Grosvenor House Hotel at the Grosvenor House Art and Antiques Fair for a week from Thursday.

Signed with Engleheart's distinctive 'E' monogram, it is one of only two portraits of Lefroy known to exist and has an asking price of around £50,000.

Gloucestershire dealers Judy and Brian Harden, who are selling the painting, said they had bought it at auction some time ago without realising its significance.

'We didn't know who Tom Lefroy was when we bought it - it went through the auction house unrecognised - but we were able to identify and discover the history of the sitter,' Mr Harden said.

Lefroy met Austen while visiting his uncle and aunt in Hampshire. They were much taken with one another, talking, dancing and apparently flirting.

She referred to him in a letter as 'a gentlemanlike, good-looking, pleasant young man' and found only one fault with him - 'his morning coat is a great deal too light'.

Romantic fiction: Colin Firth as Fitzwilliam Darcy with Jennifer Ehle as Elizabeth Bennet in the 1995 TV dramatisation of Jane Austen's Pride And Prejudice

Lefroy's parents, sensing Austen was contemplating a future with him, whisked the young law student away and the couple never met again.

Just before they parted, she wrote: 'At length the day is come on which I am to flirt my last with Tom Lefroy ... My tears flow as I write at the melancholy idea.'

Three years later he married heiress Mary Paul and had a successful legal career, becoming chief justice of Ireland. He named his eldest daughter Jane.

Austen is thought to have used her own experiences of romance - good and bad - in her novels.

Inspiration: James McAvoy portrays Lefroy with Anne Hathaway as Austen in last year's Becoming Jane

Literary historians believe Lefroy's family provided the basic plot for Pride And Prejudice and Tom himself was the inspiration for Fitzwilliam Darcy, the handsome, intelligent man who eventually married Elizabeth Bennet, the main female character in the novel.

He was played by Colin Firth in a BBC TV dramatisation in 1995. Lefroy himself has been played by James McAvoy, opposite Anne Hathaway as Austen, in last year's movie Becoming Jane.

Despite attracting several suitors, Austen never married and died in 1817, four years after Pride And Prejudice was published.