NEW YORK (Reuters) - Admiral Horatio Nelson's one-sleeved undershirt, possibly the only piece of the British war hero's clothing still in private hands, will be auctioned off next month in London, Sotheby's said on Friday.

The beige undershirt, with an "N" embroidered inside the neck and its right sleeve cut short, is expected to fetch between $500,000 (281,700 pounds) and $900,000.

Other Nelson relics and rare letters, including a 10-page epistle to his mistress Emma Hamilton, will be placed on the auction block as part of a collection celebrating the 200th anniversary of the Battle of Trafalgar.