The Simpsons
Judd Apatow wrote an upcoming episode of "The Simpsons," titled "Bart's New Friend." Fox Flash

Judd Apatow is disproving the adage that a writer’s first attempts aren't worth reading. In the “Knocked Up” creator’s case, it just takes the better part of two decades before anyone realizes it's good. In 1990, the filmmaking funnyman wrote a spec script for “The Simpsons,” and now that script has come to life.

Most writers in Hollywood have a litany of spec scripts lying around that never went anywhere. However, the “Girls” executive producer mentioned his “Simpsons” script in an interview a few years ago that was read by Al Jean, of the show’s executive producers. Apatow and Jean had worked together on Jean’s short-lived animated comedy “The Critic,” and after reading the interview, he told Apatow that now was the time to make his dusty spec script happen.

Apatow submitted the script for the episode -- titled "Bart's New Friend" and set to air Jan. 11 -- when “The Simpsons” had only aired its first six episodes. It focuses on Homer being the subject of a botched hypnosis act. He’s left thinking he’s a 10-year-old boy and immediately befriends his son, Bart. The family has difficulty getting Homer to return to normal because he's enjoying being a kid. In an interview with Entertainment Weekly, Apatow claims the plot was something he’s had trouble getting away from.

“The reason I brought up the 'Simpsons’ episode is because I realized while doing this interview that everything I had ever written was the premise of the first thing I had ever written,” said the creator of "The 40-Year-Old Virgin" and "This Is 40." “All of my stories are about people trying hard not to grow up.”

Apatow admits his script needed the current "Simpsons" writing team to make it fit for television.

“It's a pretty rough script — when I reread it I wasn't exactly glowing with pride — but Al and the staff did their Simpsons magic on it,” he said in an interview with TV Guide. “The whole process blew my mind. Sitting at the table read, listening to Dan Castellaneta [Homer], Julie Kavner [Marge], Nancy Cartwright [Bart] and Yeardley Smith [Lisa] putting their brilliant spin on something I wrote back when I was a dreamer, was one of the greatest days of my life.”

This actually isn’t the first time Apatow has been called upon for an episode of “The Simpsons.” Earlier in 2014 he lent his voice to the episode titled “Steal This Episode,” in which he played one of Hollywood’s elite brought in to chastise Homer for showing pirated movies in his backyard.

Apatow’s episode will air Sunday, Jan. 11, at 8 p.m. EST on Fox.