Ever sinceThe Walking Deadcomic book debuted in October 2003, fans have been wondering what exactly caused the series' zombie outbreak.The Walking Deadseries creator Robert Kirkman has consistently said that the origin of the zombie virus wouldn’t be explained in the comics, insisting that its origin was ultimately pointless to the story being told. Despite this, Kirkman has said that he himself knows what caused the virus, and that he may reveal it randomly at some point in a future interview. Well, Kirkman may have finally revealedThe Walking Deadzombie virus origin, though it’s possible he’s just joking.

On Twitter, a fan asked Kirkman what caused the zombies inThe Walking Dead, and he responded, “Space spore.” What’s interesting about this answer is thatKirkman’s pitch forThe Walking Deadseriesto Image Comics said that aliens were behind the zombies, using the undead to “weaken the world’s infrastructure” before invading. Kirkman had no intention of going through with the alien invasion pitch (it was just a lie to get the series approved), so his “Space spore” explanation could just be an extension of that joke.

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While the origin of the zombie virus inThe Walking Deadmay not be that interesting to Kirkman himself, it’s understandable why fans want answers.The Walking Deadis a massive media franchise after all, having extended to basically every form of media imaginable, including video games.

Telltale’sThe Walking Deadgames have been huge hits, and there’s also a popular augmented realityWalking Deadgame available as well. OtherWalking Deadvideo game projects haven’t had quite the same success, though one recent release is rather impressive.

The Walking Dead: Saints and SinnersVR gamejust launched for PC-powered VR headsets and is earning decent reviews. If nothing else, it shows that there is still a lot more quality content to mine fromThe Walking Deaduniverse, so even with the comic book series over and the AMC TV series no longer at the height of its popularity, fans should be able to look forward toWalking Deadcontent for years to come.

Whether or not any of thisWalking Deadcontent ever provides a proper reveal for the zombie virus remains to be seen, however. For now, fans may have to be satisfied byRobert Kirkman’s “space spore” answer until they hear something different.