There's a mistake in The Simpsons that even the most hardcore of fans may have missed.
In season six episode 13, when Marge tells Homer she's pregnant with Maggie, Maggie's picture appears to already be framed on the wall behind them.
Executive producer Matt Selman tweeted the error from "And Maggie Makes Three" to fans yesterday.
While some argue the picture is of Lisa, not Maggie, others say the show predicted the future.
Maggie is in photo on wall behind Marge telling Homer she’s pregnant with Maggie pic.twitter.com/uckWDl8qWp— Matt Selman (@mattselman) September 5, 2018
It seems Matt isn't the only person working on the show who didn't realise the mistake.
Al Jean, another writer on The Simpsons, appeared to have also not realised, tweeting: "Canon is in ruins!"
And Yeardley Smith, who voices Lisa Simpson, tweeted: "Oooops".
Fans of the show have rushed to share their thoughts about the oversight, with some saying the "obvious excuse" is that the picture is actually of baby Lisa.
Baby Lisa, would be the obvious excuse— Michael Gebert (@skyfullofbacon) September 5, 2018
Others are insisting the show predicted the future, which has been a popular Simpsons theory since fans argued it predicted Donald Trump becoming president of the United States in 2000.
Simpsons predicted the future— Allie Goertz (@AllieGoertz) September 5, 2018
Fans also discovered that the show predicted Disney's takeover of 21st Century Fox 19 years before it happened.
But the Maggie Mistake isn't the only continuity error on the show.
Some have pointed out that a similar situation occurred when Marge told Homer she was pregnant with Lisa.
He runs past a picture of their daughter when she hasn't even been born yet.
I noticed this before it was cool (Marge telling homer she’s pregnant with Lisa and a photo of Lisa appears on the staircase) this was on April 27. In return I would like a cell of Homer’s arm pic.twitter.com/GpCFg7uMRs— Kevin Sousa (@RetroRelapstic) September 6, 2018
Others have spotted that an episode where Lisa is a baby includes a photo of her as a child already framed on the wall.