For 70 years or so, Alan Gershwin insisted he was George Gershwin’s long-lost son. And with his death on Feb. 27 at 91 in a Bronx hospital, the curtain came down on what was surely the Gershwins’ most bizarre show ever, revolving around whether this affable but monomaniacal man was one of the greatest victims in U.S. musical history, or a grifter running a long-term con, or someone suffering decades of delusion.

Alan Gershwin contended that sometime in the mid-1920s — the year and place varied in the telling, but once it was tracked down his birth certificate stated May 18, 1926, and the Brooklyn Hebrew Maternity Hospital, respectively — he was born Albert Schneider to a sultry dancer named Mollie Charleston, who went by the stage name Margaret Manners. His mother, by his account, was his father’s longtime paramour, whom he had met through his songwriter friend Buddy DeSylva.

Through the machinations of Ira Gershwin, George’s brother and principal lyricist, he said, he had been fobbed off on Mollie’s sister and her husband, Fanny and Ben Schneider of Brooklyn, who had pretended he was theirs. (By Alan Gershwin’s account, Mollie had masqueraded as her sister when she gave birth, so Fanny’s surname went on the certificate.)

Fortifying his sensational story were purported shards of memory, some happy — hammering out joint compositions on a piano with his father, visiting Ethel Merman with him backstage — and some not, like grim men in black limousines bringing crisp hundred-dollar bills to Brooklyn to pay for his upkeep but warning him to say nothing about it, or else.

After considerable consternation, genetically certified Gershwins and their loyalists came to see Gershwin less as a threat to their millions than as a crank and an annoyance. Occasionally, they’d reach out to squelch his periodic public appearances. Whenever scrutinized, Alan’s claim wobbled; the faith of even his girlfriend for the past 20 years, Blossom Tracy, sometimes wavered.