Warning: Potential SPOILERS for Joker ahead

Joaquin Phoenix's Arthur Fleck in Joker seems to be obsessed with the Wayne family - and it could be because he's one of them. Story clues and character details point to a serious possibility that Arthur is Thomas Wayne's son, which would make him Batman's half-brother.

When the chilling first trailer for Todd Phillips' Joker was released there was no real reason to question why the Joker and the Wayne family were at odds, since fans are so used to the idea of the Joker and Batman being enemies. But besides the general storyline of Gotham's underclass rising up against wealthy elites like Thomas Wayne, with the Joker mask as their symbol, there didn't seem to be much specifically connecting professional clown Arthur Fleck and Mayoral candidate Thomas Wayne.

Related: Dark Theories About Joaquin Phoenix's Joker

Putting together the pieces, however, the trailer fits well with a story about a rejected son seeking vengeance for both himself and his mother, against the wealthy man who left them both in poverty, and the younger brother who had everything.

Thomas & Bruce Wayne's Role In Joker Movie

Joker Trailer - Thomas Wayne on a Train

The original character description for "Mr. Warner" (the name used for Thomas Wayne in casting) described him as "male, Caucasian, 60s, a deeply-tanned, hair dyed so black it was almost blue, highly successful, New York City businessman, rumored to be running for Mayor. He’s a public figure in the city and a symbol of wealth." Thomas Wayne is played by Brett Cullen in the movie, though Alec Baldwin was originally cast in the role, as Phillips had been seeking to portray Wayne Sr. as a Trump-like figure (Baldwin famously plays Trump on SNL). Meanwhile, the young Bruce Wayne is played by Dante Pereira-Olson.

Thomas Wayne is indeed running for Mayor, as prop posters spotted on the set of Joker first revealed, but he doesn't appear to be a popular public figure. The trailer showed a protest taking place outside the Wayne Building, and set photos revealed placards with messages like "Blame Wayne" and "Fascist Wayne is to Blame." A shot in the trailer also showed Thomas Wayne being attacked by a mob wearing Joker masks in a subway station, while the clown himself casually sauntered away, and during the protest outside the Wayne Building we see Arthur getting thrown down the stairs. Clearly, Arthur's alter ego is the flashpoint for this outburst of anti-Wayne sentiment, and the reasons could be very personal.

Is Thomas Wayne the Joker's Father?

Joker - Arthur and Penny

The key to this theory is Arthur's mother, Penny Fleck, who is played by Frances Conroy. As shown in the trailers, Arthur still lives with his mother in what looks like a small apartment. We see him dancing with her in front of the television, and washing her hair in the bath. The two of them are clearly very close - possibly unhealthily so.

Related: Joker Trailer Breakdown: 15 Story Reveals & Secrets

An early character description for Penny described her as, "very attractive in her youth, obsessed with her former employer and unable to believe this is what her life has come to." The second part of that is key, as there's a good chance that Penny's "former employer" was Wayne Enterprises (this alone would explain Arthur's resentment towards the Wayne family). Conroy and Cullen are both in their sixties and Phoenix is in his forties, which means the timeline certainly fits with a classic story of a privileged young heir having an affair with one of his company's employees, resulting in a pregnancy.

From there we can theorize that the naive young Penny Fleck was dismissed and silenced by Wayne Enterprises in the interests of protecting young Thomas Wayne's reputation - perhaps taking a lump sum of money in exchange for signing a non-disclosure agreement, and swearing never to bring up the topic of Arthur's parentage. During one part of the trailer, a tense-looking Arthur is shown visiting Arkham State Hospital's psychiatric ward; could Thomas Wayne go so far as to have Penny Fleck forcibly committed, if she made claims abut Arthur's parentage during Wayne's mayoral campaign? That would certainly be the sort of thing that could make an already unstable man snap.

What Does Joker Being A Wayne Mean For Batman?

The enduring appeal of the Joker as a villain is that we never really know his motivation - if he even has one. Alan Moore and Brian Bolland's graphic novel The Killing Joke hypothesized the best-known version of the Joker's origin story, but its status as DC Comics canon has wavered over the years. Christopher Nolan's The Dark Knight toyed with the mysterious nature of the Joker's backstory, with the character telling two stories about how he got his scars - either of which could explain the supposed emotional trauma that led to him painting his face and becoming a terrorist. However, neither of the stories really rang true, and there was a definite sense that they were simply another one of the Joker's games.

If the theory about Phoenix's Joker being the illegitimate and ignored son of Thomas Wayne is true, however, then Phillips' movie could be a more straightforward tale of revenge. The trailer showed Arthur targeting young Bruce Wayne - enticing him over to the gates of Wayne Manor and then forcing his mouth into a grin. It's possible that Phillips' film is some kind of "What if...?" take on the DC universe where the Joker kills Bruce Wayne as a child and Batman is never born (or perhaps Thomas Wayne becomes Batman instead, a la Flashpoint). It's also possible that the Joker will be responsible for Batman's origins, which would be an interesting twist on The Killing Joke.

Regardless, the idea of the Joker being a Wayne would definitely shed an interesting light on the usual dynamic between himself and Batman, and would also add extra layers to his obsession with the caped crusader. And while it might sound far-fetched to suggest that Batman and the Joker could be brothers, this is just one hypothetical origin story of many - so why not go crazy with it?

More: All 30 Upcoming & In-Development DC Films

Key Release Dates