Don't hold your breath for a sequel to The Simpsons Movie: creator Matt Groening says making the first one was arduous enough that a follow-up isn't likely anytime soon. "It took us four years and it killed us," Groening said Saturday at UCLA's annual entertainment symposium, where he did a keynote Q&A with longtime Simpsons producer and director David Silverman.

"Maybe another 10, 15 years," Silverman added, according to The Hollywood Reporter. The Simpsons Movie has grossed $500 million since it hit theaters in 2007.

Q&A: Matt Groening Gets the Heck Out of 'Life in Hell'

Groening was part of an hour-long session with an audience of about 400 entertainment lawyers, where he also talked about the origins of The Simpsons and why the show has lasted more than 20 years since its 1990 debut.

"We were in the right place at the right time," Groening said, thanks to a young network, Fox, that was eager for original content. Now, Groening said, networks tend to interfere too much with animated shows. "They always try to water it down and soften it up, and that doesn't work." 

Groening credited the show's longevity to the strength of the core characters and the ever-expanding world the writers have created over the years. "We've got 400 or 500 characters, and about 50 per episode," Groening said.

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