President Trump might have ascended to the White House but there's one role he still hasn't managed to attain: guest star on The Simpsons.

A fan asked executive producer Al Jean at San Diego Comic-Con whether the animated sitcom had ever declined a celebrity's request to voice a character on the Fox fixture.

"Let's just say he's the president of the United States," Jean responded.

The panel — hosted to promote the series' forthcoming 29th season — also referenced the prophetic flash-forward episode, "Bart to the Future," which aired in 2000 but alluded to a United States where Trump was president.

Executive producer Matt Selman promised that "The Simpsons" did not only predict "terrible" events.

Creator Matt Groening also told fans at the event on Saturday they were asked to "take it easy" on Fox News after the show's writers started including jokes about the network.

"Bill O'Reilly called us pinheads and look what happened," Groening said.