Joaquin Phoenix's portrayal of Arthur Fleck saw 2019 film Joker rake in more than a billion dollars at the box office worldwide.
Although the psychological thriller directed and produced by Todd Phillips proved to be critically divisive, Phoenix himself walked away with a huge haul of gongs including the Academy Award for best actor.
But one fan has pointed out that we all missed an incredible easter egg hidden right at the beginning of the movie - which is so good it's led to others debating whether it was simply pure conincidence.
As Phoenix's character sits in front of a mirror to apply his iconic make-up, one person pointed out there's a very familiar face glaring out in the reflection.
The dark shape created by the fittings of the mirror, Arthur's position and two lights in the background appear to perfectly form the mask of his archenemy Batman.
But it didn't stop there, after another fan replied to the post on Reddit to say: "You got it upside down, flip the picture over and you can even see the lips. And it makes sense for it to be upside down since the Joker is the antithesis of Batman."
The image becomes even more clear upside down, with the light shade forming the cut out in the mask around the mouth of Batman and the colouring even appearing to form a pair of lips.
One replied to say: "I just turned it upside down and screamed. It's so perfect. HOW CAN THIS NOT BE INTENTIONAL."
A second replied: "Man, if this was intentional and sort [of] like an Easter egg, then this was a damn good one."
Another added: "Bats sleep upside down."
But others argued: "That definitely just seems like a coincidence."
Those who doubted the detail had been purposely created may have already been proven correct by film director Phillips, who has previously spoken about hiding secret signs in his movies.
"I don’t do Easter eggs. Any Easter eggs anybody finds is a mistake," he said, as reported by Collider. "I don’t understand."
Responding to fans who insist there are Easter eggs lurking in his work, he pledged if there were it would simply be the "art department sneaking something in that would make me crazy if I knew about it."
