[Photo by: FOX]

Continuity errors are a filmmaker’s worst nightmare, yet, it doesn’t seem like something that’s bothering one of the Simpsons executive producers, who shared a major error from one classic episode.

Read more: ‘The Simpsons’ becomes the longest-running scripted show in TV history

One of the show’s Executive Producers, Matt Selman, took to Twitter earlier this week to post his finding. Showing a snap from the 13th episode of the sixth season called “And Maggie Makes Three,” Selman shared that the team behind the show made a pretty big continuity error.

In the episode, Marge shares with Homer that’s she pregnant with the pair’s third child, Maggie. While nothing would seem out of the ordinary in the episode, you might have noticed a photo of Maggie was already hanging on the wall.

Noticing the mistake, Selman took to Twitter to share his revelation, saying:  “Maggie is in photo on wall behind Marge telling Homer she’s pregnant with Maggie.”

While the continuity error is pretty huge, that can be expected from a show that’s been around for almost 30 seasons, and it has us wondering what other mistakes could be hiding in the show’s many episodes.

Did you ever notice this big Simpsons error? Let us know in the comments below!

The Simpsons will be making their on-air return on FOX this Sunday, Sept. 30 at 8:00 p.m. ET.