Manuscript DS, signed “F. S. Key,” one page both sides, 8 x 3, June 8, 1814. Promissory note reads, in full: “Three months after date I promise to pay Francis S Key Esq or order two hundred forty dollars and fifty-four cents value received.” Signed at the conclusion by James S. Morsell, and signed on the reverse, “F. S. Key.” Two other dates on the reverse read, “Sep 8 1814,” and “Sept 12,” indicating the debt was paid. In very good condition, with intersecting folds, with a horizontal fold lightly passing through signature, several ink cancellations to front, with one slightly showing through under signature, and scattered toning. After securing the release of Dr. William Beanes on September 7, Key and John Stuart Skinner were detained by the British after hearing about the British plans to attack Baltimore in a few days. On September 13, the British began a twenty-five hour bombardment of Baltimore’s Fort McHenry, and Key witnessed it from the warship. The following day, Key saw a giant American flag still waving over the American fort and was inspired to write his famous poem on the back of a letter he was carrying. Key was released on September 16th, and his composition, originally entitled ‘The Defence of Fort McHenry,’ was published the next month. Most likely, Key signed this promissory note within days of his release by the British. Pre-certified PSA/DNA and RR Auction COA.