Pocket watch, (now mounted as a carriage clock) worn by Nelson at Trafalgar, which is estimated at £250,000-450,000 at Sotheby's.

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Specialists at auction house Sotheby’s believe Nelson either acquired the pocket watch or he received it from an admirer following the Battle of the Nile in 1798, and that he carried it during Trafalgar.

Nelson was killed after a French sniper’s bullet pierced his shoulder and shattered his spine during the battle and this watch was removed while he was on the flagship, HMS Victory.

It is being offered on July 4 with an estimate at £250,000-450,000.

The Emery pocket watch No. 1104 is now mounted in a gilt-brass carriage clock case and was made by Georgian watchmaker Josiah Emery (c.1725-97).

Even without the Nelson provenance the watch would be valuable as Emery, a Geneva watchmaker who set up in London, is renowned for his fine timepieces.

It was not part of the sale of Nelson artefacts sold in July 1895 and acquired for the nation by the British government. The watch is now one of only a small handful of Nelson possessions still in private hands.

When Nelson died this watch was one of 19 objects returned to his mistress, Emma, Lady Hamilton, following his death. It was then inherited by the admiral’s brother, William, 1st Earl Nelson, and subsequently passed to his sole surviving child, Charlotte. She arranged for the watch to be mounted in its current form as a carriage clock.

The watch, which has previously been on loan to the National Maritime Museum in Greenwich, had remained under the ownership of Charlotte’s descendants until it was bought by a private collector in the US. It is now being offered following the collector’s death last year.