(CNN)A rare note written by a doctor who treated Napoleon Bonaparte has revealed how the French military leader and emperor suffered with sickness and pain in the years before his death.
The letter, dated June 4, 1818, was written by Irish surgeon Barry Edward O'Meara, who treated Napoleon when he was in exile on the remote South Atlantic island of St. Helena.
Remarking on Napoleon's "ill health," the letter describes how he was "experiencing severe corporeal sufferings," including a headache, pain in his right hand side, a "considerable" fever, a racing pulse and "general anxiety and oppression."
In the letter, which has been sold by Heritage Auctions in Texas to an unnamed British citizen for $2,000, O'Meara also revealed he had to remove one of Napoleon's upper left teeth after he was "tormented" with toothache.
According to historians, the French emperor and O'Meara were friends, with the latter a senior surgeon on the HMS Bellerophon when Napoleon surrendered in 1815 following his defeat at the Battle of Waterloo.
Napoleon requested that O'Meara become his doctor during his exile, historians say. The British government ordered O'Meara's return in July 1818.
Napoleon, who ruled France for 15 years, died on St. Helena in 1821 and is widely believed to have succumbed to stomach cancer.
A Heritage Auctions spokesman told CNN the letter was "rare" and "in fantastic condition considering its age and travels."
Meanwhile, Sandra Palomino, director of historical manuscripts at Heritage Auctions, added it offered "a fresh and unique look inside the life of the great French statesman and military leader, so its historical importance cannot be understated."
"It's a rarity for certain," she added.
Interest in Napoleon endures to this day. In 2019, archaeologists uncovered a one-legged skeleton in Russia believed by historians to have been one of his generals, Charles-Etienne Gudin.
The team of French and Russian archaeologists discovered the 200-year-old skeleton during an excavation in the Russian city of Smolensk, around 250 miles west of Moscow.
And in 2018, a hat said to have been worn by Napoleon at the Battle of Waterloo sold for more than $400,000 at an auction in Lyon, France. The hat was believed to be one of about 120 two-cornered military dress hats worn by Napoleon.