Warning: This post contains major plot spoilers for “Joker.”

Are they bat-bros?

Perhaps no question lingers on the mind more after watching “Joker” than whether the young Batman-to-be, Bruce Wayne, and Arthur Fleck, the eventual Joker, are siblings.

Director-writer Todd Phillips does not stick to the comic-book rules of Batman, which are normally written in stone — golden rules such as the Dark Knight never killing — and creates a scenario certain to have some fans screaming in protest.

While many moments in “Joker” can be attributed to Fleck’s descent into madness, none is quite as stinging as the is-he-or-isn’t-he aspect of his relationship with Bruce Wayne’s father, Thomas.

Fleck’s mother, Penny, once worked for Thomas Wayne. She was dismissed after being diagnosed with mental issues. But who did the diagnosis? Were the struggles that plagued her and affected Fleck’s childhood brought on by true health issues? Or were her problems the result of Thomas Wayne using his immense wealth and clout to cover up something he thought might have a negative effect on his family fortune?

There are whiffs of a potential father/son conflict when Fleck, after introducing himself to a young Bruce Wayne outside Wayne Manor’s protective gates, confronts Thomas Wayne about Penny’s health issues and the uncertainty of his paternity. There’s another heated meeting between Fleck and the elder Wayne at a movie theater, which results in Wayne clobbering Fleck with a punch that seems anything but paternal. Both times, Wayne insists that Fleck’s mother was insane and that there is documentation to prove it.

Indeed, one of “Joker’s” most emotional moments comes when Fleck gets a hold of the mental records for his mother and Wayne’s words sting true: It’s all there in writing that she was not well and hadn’t been for some time.

It’s an “aha” moment, one that gives viewers a minute to catch their breath and realize a brotherly connection between Bruce Wayne and the Joker is just a figment of their imaginations.

Or is it?

Near the end of the film, with his transformation into a villain almost complete, Fleck looks at a photo of his mother from her youth. She’s beautiful. Full of life. The image of a woman who is sure of herself. On the back of the photo is a handwritten note — from Thomas Wayne. He mentions how much he loves her smile. The words are few, but flirtatious enough to make you wonder yet again.

Fleck isn’t the only one whose mind is playing tricks on him.

Thomas Wayne is a powerful man — powerful enough that he could have put up money to forge documents that certify someone as mentally unwell. Of course, a quick episode of “Maury” and those reliable DNA tests could solve everything, but Fleck has already killed his mother, convinced she was the crazy one. Now entering the initial levels of his permanent psychosis, Fleck has unwillingly assured that no one will be asking those types of questions.

The Joker and Bruce Wayne are definitely still intrinsically connected in one way. The Joker’s chaos starts a movement in Gotham City, creating a war of the haves and have-nots with clown-mask-wearing rioters everywhere. One of them gets a look at Thomas Wayne and his family leaving the theater. Wayne and his wife are gunned down, creating the dark and iconic moment that eventually gives birth to Batman.

But “Joker” never gives us clarity as to whether this was truly a family affair. Did Thomas Wayne bring his downfall on himself? Are the Joker and Bruce Wayne more than destined enemies — bonded not just by blood, but a bloodline?

The movie goes out of its way to make it so you can’t be sure. And because this film intentionally isn’t inspired by the comics of the Batman mythos, it’s up to you to decide whether there’s a deeper connection between these future enemies.

It’s pretty mind-boggling. Just like a Joker movie should be.

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