It's one of the best-loved musical films of all time, and it's airing on ITV1 this afternoon.

Fans will undoubtedly be familiar with the 1978 movie from start to finish, but a very dark new theory has blown the internet's mind.

Remember Summer Nights when Olivia Newton-John's Sandy sings of her time with John Travolta's Danny? In the lyrics, she reminisces about how Danny saved her from drowning.

Apparently, he never managed to save her, so the entire movie is her dying dream...

Fans on Reddit have highlighted how Summer Nights ends with the line "goodbye to Sandra Dee", suggesting she's in the process of drowning. The Reddit user's other piece of evidence is the all-too perfect ending in Grease. They wrote: "Danny and Sandy are back together despite everything. Rizzo suddenly isn't pregnant and Kenickie suddenly decides that he actually loves her [and] the geeky kid gets onto the sports team. EVERYTHING is suddenly ok, just the way that sweet, innocent Sandy would have wanted it to be."

Then there's the flying car which presumably ascends into heaven? Some fans weren't impressed by the theory with one suggesting it was Danny who was dying. The alternative theory suggests Danny was drowning in an attempt to save Sandy. As he dies he gives the girl the name Sandy because they're by the beach and imagines a perfect romance where he builds his dream car and graduates high school. Maybe a little too dark?