One of 2019's most popular movies was Joaquin Phoenix's Joker, which made over a billion dollars at the worldwide box office.

Joker was directed and produced by Todd Phillips, and while it was critically divisive, it still managed to earn Phoenix a number of awards, including the Academy Award for Best Actor.

If you haven't seen it yet, this is the trailer for Joker:

[[jwplayerwidget||https://content.jwplatform.com/videos/cRUk8WtE-Q0L14jDU.mp4||cRUk8WtE]]

However, it turns out that while the movie has been watched countless times, there was one Easter egg that wasn't spotted until now, and it can be found right at the start of the movie, causing many fans to speculate whether or not it had been placed there deliberately or if it was just a coincidence.

You can spot the Easter egg in the scene where the Joker applies his makeup in front of a mirror, and if you look closely enough, Batman's face is staring back...

An Easter egg in Joker. [[imagecaption|| Credit: Reddit]]

However, the speculation didn't stop there, and one person took to Reddit to write: "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 of the Batman becomes even more noticeable when its viewed upside down, with the light showing Batman's mask and the light even appearing in the shape of his lips.

One Redditor replied to say: "I just turned it upside down and screamed. It's so perfect. HOW CAN THIS NOT BE INTENTIONAL."

A second wrote: "Man, if this was intentional and sort 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."

Joaquin Phoenix. [[imagecaption|| Credit: PA Images]]

The movie's director, Phillips, has previously spoken about the existence of Easter eggs in his films.

Collider reported him saying: "I don’t do Easter eggs. Any Easter eggs anybody finds is a mistake. I don't understand."

When asked if there are any hidden Easter eggs in his work, he said that if they exist, they would be the product of the "art department sneaking something in that would make me crazy if I knew about it."

So, is this just a coincidence or is Phillips hiding just how much of a genius he truly is?

Fans spot familiar face staring back at Joaquin Phoenix in 'Joker' Easter egg