The letter, by the English naturalist best known for his contributions to evolutionary theory was in response to a frank question posed by Francis McDermott, a barrister, who wrote on November 23, 1880: "If I am to have pleasure in reading your books I must feel that at the end I shall not have lost my faith in the New Testament. My reason in writing to you therefore is to ask you to give me a Yes or No to the question Do you believe in the New Testament."
Two days later Darwin responded by writing: "Dear Sir, I am sorry to have to inform you that I do not believe in the Bible as a divine revelation & therefore not in Jesus Christ as the son of God. Yours faithfully."
Darwin's letter remained unknown for over 100 years, with McDermott keeping to his promise not to publicise Darwin's highly controversial reply for the time in "theological papers".
When studying at Cambridge to become an Anglican clergyman, Darwin did not doubt the literal truth of the Bible, but his views began to change after he took his history-making nautical voyage around the world on the Beagle.
He returned to write "The Origin of Species" in 1859, the book that would detail his theory of evolution through natural selection, sparking debate and prompting questions over Darwin's religions views.
It has been claimed that Darwin reverted to Christianity on his sickbed. The claims were repudiated by Darwin's children and have been dismissed as false by historians.