The Simpsons finally have an answer to major Homer mystery that's been puzzling fans since the first episode 35 years ago

Warning: This article contains spoilers of The Simpsons, season 36, episode four

You'd think after 772 episodes, The Simpsons would be out of any remaining mysteries - but that doesn't seem to be the case.

Asides from the show's uncanny ability to seemingly 'predict' the future, there's some parts that we've just accepted over the years - like of course, Maggie gets scanned in the opening sequence?

But there's one long-running gag that viewers have been wondering about for a while now.

And that's how Homer Simpson - despite being the world's worst employee - has managed to keep his job at the Nuclear PowerPlant for so long.

I assumed it was just because he was the main character of the popular sitcom and that it was purely satirical - that was until yesterday (October 27).

Prior to the release of the fourth episode of season 36, named 'Shoddy Heat', show runner Al Jean tweeted: "Tonight new @thesimpsons with long running mystery solved at this point in the show."

Now, viewers were finally given the answer to the mystery of why Mr Burns had never sacked his worst employee.

And this mystery involves Homer's dad, 'Grandpa' Abe Simpson.

After four decades on the air, The Simpsons have no shortage of mysteries (Fox/Disney)

Back in the 1982, Grandpa worked as a private detective alongside his partner Billy O'Donnell, when they were asked by Agnes Skinner, Mr Skinner's mom, to investigate her boyfriend, Mr Burns.

Agnes wanted to know whether he was cheating on her, but during O'Donnell's investigation, he vanishes.

Grandpa goes round to Mr Burns' manor demanding answers, to which Mr Burns replies that O'Donnell had 'gone to paradise' - a phrase which sounds straight out of The Godfather.

To prevent Grandpa from squealing, Mr Burns makes a deal with him whereby he would hire Homer at the power plant and he wouldn't fire him no matter how badly he screwed up - even a specific total of '742 times'.

Homer then realized everything his father did for him and thanked him as he recalled all the times where he should have been fired.

This sign takes on a whole new meaning, huh? (Fox/Disney)

However, there have been instances where Homer has been sacked before, like in 'Homer's Odyssey', 'Burns Verkaufen der Kraftwerk' and 'Diatribe of a Mad Housewife', or when he has left willingly, like in 'Maggie Makes Three' where he quits to pursue his dream job at the bowling alley.

However, he is always brought back.

Taking to Twitter to discuss the show, one person wrote: "Kudos to the new episode for revealing the answer to the question, 'How come Homer never got fired from his job despite all the mistakes he made?' in the most surprising & weirdly wholesome fashion possible."

Although, not everyone was a fan, as another wrote on the social media platform: "Did not really care for tonight's new episode of #TheSimpsons, 'Red Heat'; this is not the first time the show, in recent years, has done a 'Grampa actually has a more interesting past than we thought' plot and I am sure it is not the last; didn't really find it interesting."