The presentation copy of Emma that Jane Austen sent to her close friend Anne Sharp. It will be offered at Bonhams on June 24 with an estimate of £50,000-70,000.

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Jane, who deplored George's conduct and profligacy, was nevertheless rational enough to recognise the potential benefit and was persuaded by her brother Henry and sister Cassandra that this was more a royal command, or an obligation than suggestion.

John Murray, who had not so far been exactly rushing into print, agreed and the book was indeed dedicated to the Prince Regent. One of the dozen presentation copies that she was allowed by her publishers was handsomely bound and duly sent to him.

According to one of Jane's recent biographers, David Nokes, Jane had one copy sent to Maria Edgworth (who failed to acknowledge the gift and in private conversation was disparaging about Jane's writing) and another went to Countess Morley, a new friend and someone who had once been widely rumoured to be the true author of Pride and Prejudice. The remainder were earmarked for members of her family but one was reserved for an older and much-loved friend.

This was Anne Sharp, whom she had first met in 1805 at her brother Edward's house at Godmersham. At the time Anne was employed there as a governess, but though she moved to the north of England the following year, eventually setting up her own boarding school in Everton, the two women had taken to each other at once and kept up a regular correspondence for the rest of Jane's life.

Claire Tomalin, in her Austen biography, writes of a truly compatible spirit and of Anne's unique position as "...the necessary, intelligent friend". One of Jane's last letters was addressed affectionately to Anne and, following her death, her devoted sister Cassandra sent Anne a lock of Jane's hair.

Jane always took seriously Anne's reactions to her novels and commented in her record of reviews and suchlike, "she liked it better than M.P. - but not as well as P.&P. - pleased with the heroine for her originality, delighted by Mr K. - & called Mrs Elton beyond praise - dissatisfield with Jane Fairfax".

No presentation copies of Emma have ever come to auction and it is not entirely clear how many survive, but on June 24 Bonhams will sell the copy that she asked John Murray to send to Anne.

In contemporary half calf, it is inscribed From the author (by the publisher) to the flyleaf of the first volume and all three bear Anne Sharp's ownership signature.

The anonymous British vendor of the book said, "The novel had been sitting in my family library for at least three generations and it remains a mystery as to how the book first got there", but that mysterious arrival is now expected to sell for something in the region of £50,000-70,000.

By Ian McKay