The old episodes of “The Simpsons” are the best, full of hilarious gags, brilliant characters, and compelling stories, but it turns out they also contain a mistake or two.

One of the offending episodes is the season 6 classic, “And Maggie Makes Three”, where Homer and Marge tell the story of how Maggie was born. The episode plays out in a series of flashbacks.

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In the scene where Marge reveals that her contractions have started, there is a framed photo of Maggie hanging on the living room wall in the background — a crucial error given she hadn’t been born yet.

The gaffe was spotted by “Simpsons” executive producer Matt Selman, who tweeted a screengrab of the moment.

While some fans tried to come up with reasons for the blunder — maybe it was a baby photo of Lisa — the “Simpsons” crew openly admitted to the error.

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“Canon is in ruins,” producer Al Jean said:

Yeardley Smith, the voice of Lisa Simpson, also got in on the action:

However, the Maggie photo isn’t the only mistake of the episode, as pointed out by Metro, in the scene where Marge tells Homer she is pregnant with Bart, he is seen running up the stairs past a picture of Lisa, who, again, has yet to be born.