The letters written by Josephine de Beauharnais, the first wife of Napoleon Bonaparte, to his trusted general Alexandre Berthier, will be auctioned by Sotheby's in Paris on Tuesday.
The letter is one of four revealing unpublished letters from Josephine to Berthier - held within his family for more than two centuries.
Frederique Parent, an expert at the Paris branch of the auction house, said that these were wonderful letters, and were intimate and revealing, to a man who was a trusted friend, the Guardian reported.
Beauharnais apparently wrote in October 1806 that Berthier needs to take care of the emperor and to ensure that Bonaparte does not expose himself too much, as he was one of his oldest friends and it is their attachment to the emperor that calmed her.
The auction that predicted to raise several million euros, also included uniforms and swords, family portraits and records, books and documents spanning Berthier's career.