The letter was found in a country house in Gloucestershire, where it has remained for decades and therefore has never been seen by the public before.
Lord Byron is the most infamous poet of the 1800s for his work spearheading the Romantic Movement and his controversial personal life.
He was rumoured to have had a child with his half-sister, affairs, debt, and also a pet bear.
He travelled widely in Europe living for seven years in Venice, Ravenna, and Pisa after he was forced to flee England due to being threatened with lynching over his failed marriage, scandalous affairs and huge debts,
He died aged 36 in 1824 after contracting a fever whilst leading a campaign against the Ottoman Empire in the Greek War of Independence.
The letter has come to auction along with one from 18th century Swiss philosopher, composer, author and political theorist Jean Jacques Rousseau, surprisingly also discovered in the UK.
Chorley’s auctioneers – based in Prinknash Abbey – discovered this rare letter on a routine valuation day, brought in by an owner who had no idea what they were in possession of as it was written in French.
After further inspection and translation experts authenticated the letter and signature as being from a political influencer of the Age of Enlightenment Rousseau.
He was writing to Prussian diplomat Monsieur Le Chambrier to ask for help with a woman’s plight following a fire.
The letters are set to make a combined £7,500 at auction in the Spring.
Lord Byron’s letter is the only letter ever written by him to Major John Cartwright, an English politician and political reformer who served under Lord Byron’s father in the navy.
He petitioned for parliamentary reform for most of his life which is how he got the well-known title as the ‘Father of Reform’.
The letter is an apology from Byron for cancelling plans with Major Cartwright at the last minute on June 26th 1813.
It reads: “Dear Sir, It is with great regret I find that it will be necessary for me to leave London tomorrow morning – and thus be prevented the pleasure I had promised myself in meeting you & Sir F. tomorrow.
“I was not aware of this till the Post came in this morning, which must be my apology for not acquainting you with the circumstances before. I am truly yrs B”.
This letter is estimated to make between £1,500-£2,500 at Chorley’s Auctioneers when both letters go up for sale on March 20, 2024.
Werner Freundel, Director at Chorley’s said: “The discovery of a letter featuring two such important historical figures in Britain is thrilling, as both contributed so much to our society and the Britain we know today.
“This letter shows a human insight into Byron’s extraordinary character and knowing the background to his life at the time, makes it all the more interesting.
“We hope that it is purchased and retained in its present condition, hopefully in the public eye, for many years to come.”
Rousseau’s letter, from the 3rd of February 1763, reads: “I have the honour Sir while begging you to grant consideration while assuring you at the same time that I am your humble and obedient servant Jn Js Rousseau”
The amazing find is estimated to make between £3,000-£5,000 at auction.
Mr Freundel added: “Letters involving Rousseau are exceptionally rare, so for one to be found in the UK is highly unusual and for this reason we anticipate a lot of interest, not just from here, but from abroad.”