While being interviewed for The Weekly With Charlie Pickering, Groening was totally open about the major cameo.
"You don't have to put it in quotes," he said. "We really did have him." Then he went on to recount how the guest spot came about:
"Here's the weird thing. I was sitting in the office late at night, the phone rings, and I pick it up. [I say], 'Hello?' [The person on the other end says], 'Hi, this is Michael Jackson.' And I said, 'Click' [hanging up], right? And [they] call back [and say], 'No, it really is. Don't hang up.' Because he has a voice like somebody doing a Michael Jackson bit. And he said that he loved Bart and wanted to be on the show."
The theory began in 1991 after the airing of the third-season episode "Stark Raving Dad," where Homer (Dan Castellaneta) finds himself committed to a mental institution. There he meets a large man with a soothing voice (akin to Jackson's) named Leon Kompowsky, claiming to be the Michael Jackson. He calls the Simpson residence and speaks to a skeptical Bart (Nancy Cartwright), who asks him to list his last four dates to the Grammys. When the man answers correctly, Bart exclaims, "Shiver me timbers! You are Michael Jackson!"
When the episode (directed by Wreck-It Ralph's Rich Moore) first aired, the voice of the character was credited with the alias John Jay Smith, but fans still suspected that they were able to nab Jackson for the role.
However, he couldn't be credited outright due to some sort of deal with his record company. As a result, when it came time for Kompowsky to sing Lisa's birthday song, a sound-alike had to be brought in. Even so, Jackson monitored the sound-alike's voice recording to make sure it was accurate and actually sounded like him.
"The guy was so nervous," Groening said.