Genealogy Blog produced evidence in 2004 that the lyrics for Dwight B. Latham and Moe Jaffe's song "I Am My Own Grandpa" (a.k.a. "I'm My Own Grandpaw") were derived from a Mark Twain anecdote. Twain, in turn, seems to have borrowed his anecdote from an item first published in American newspapers in March of 1822, and copied from the London Literary Gazette. (The copy below is from the Republican Chronicle of Ithaca, N. Y., Apr. 24, 1822.) As it turns out, the novelty song was based on a true story.
A proof that a man may be his own Grandfather.—There was a widow and her daughter-in-law, and a man and his son. The widow married the son, and the daughter the old man; the widow was, therefore, mother to her husband's father, consequently grandmother to her own husband. They had a son, to whom she was great-grandmother; now, as the son of a great-grandmother must be either a grandfather or great-uncle, this boy was therefore his own grandfather. N. B. This was actually the case with a boy at a school in Norwich.—Lond. Lit. Gaz.