This article contains spoilers.

As named in the home video release’s special features, there are primarily two types of monsters in William Eubank‘s creature feature Underwater: the “Clingers” and the massive “Behemoth.” The latter monster, as his name suggests, is the true “Big Bad” of the movie, and his unexpected presence paves way for one hell of a final act we can’t say we ever saw coming.

If you thought the “Behemoth” looked quite a bit like one of the most iconic monsters in pop culture, well, you’d be hitting the nail right on the head. As he revealed during an interview earlier this year, William Eubank indeed drew inspiration from the tales of H.P. Lovecraft for Underwater. Namely, his film’s final act monster is, for all intents and purposes, Cthulhu.

Lovecraft’s most iconic creation is actually in the public domain, allowing for Eubank and his visual effects team to bring the monster to the screen in their own movie – which, aside from the appearance of Cthulhu at the end, certainly doesn’t outright adapt any of Lovecraft’s stories. Speaking with YouTube’s Mr. H in January, Eubank spilled the beans.

“Yeah, spoiler alert, this is a secret Lovecraft love story, where you get to see Cthulhu briefly at the end,” he revealed.

Yes, Kristen Stewart battles Cthulhu in a movie that ultimately ended up being released by Disney. If that doesn’t make Underwater one of the year’s coolest movies so far, well, I’m not sure what would. But how exactly did Eubank manage to slip him in there without any of us knowing? And how did Disney feel about releasing a straight up Cthulhu horror movie?

Well, for starters, Underwater was very much not originally conceived as being one.

“It wasn’t written to be a Cthulhu movie,” Eubank explained in a conversation with Bloody Disgusting this week. “Brian Duffield wrote this terrific, scary film, but it wasn’t Cthulhu. It was just called a Behemoth. And I was in post for two years, basically. And during that time, when [we] actually started designing and creating what this Behemoth was gonna look like, I just knew at that point the movie was more mystical; in the way we shot it, in the way there were so many unanswered questions.”

“I knew that the best way to service that was to head towards Lovecraft.”

Backtracking a little bit, the creatures in Underwater changed a good deal during the course of that two years of post-production, and it was when the design of the “Clingers” – parasite-like beings that hang off the Kaiju-sized Behemoth – changed that Eubank realized he had the perfect opportunity to bring the ultimate scary monster into his aquatic horror film.

“[IT director] Andy Muschietti had come down and seen some of my early monster stuff, which was a little more squid-like. And he was like, ‘I don’t think that’s scary enough.’ And Chernin [Entertainment] was telling me [the same thing]. And so then I was like, alright, well… I’ll make him something that’s pretty scary,” Eubank recalls, laughing. “We didn’t have much money to do big redesigns or anything like that, but fortunately since it was early in the process we were able to tweak the design that we were doing. And obviously you see the Clingers a lot more. And fortunately because we were working on the movie in order, we were able to shift the designs towards a darker, more Lovecraftian thing. When I started submitting designs for the Behemoth at the end, I was basically just telling the artists, ‘Alright, let’s make the Old One. Let’s get the boss of all bosses.’ It all worked. It’s so perfect.”

Eubank continued, “Disney then bought Fox, and we went into hibernation – I didn’t really know what was happening with the film. And we get to the first marketing meeting and one of the first marketing points was, ‘We think Lovecraft fans are going to love this movie.'”

“Right away Disney was getting it. They understood what we had done.”

Ultimately, Disney released Underwater without ever tipping their hand to Lovecraft fans, and Eubank is thankful that the marketing preserved the secret at the bottom of the ocean.

“In order to make a proper Cthulhu movie, in my opinion, you can’t say it’s a Cthulhu movie,” he told us. “Because then the experience of the unknown and the cosmic horror really isn’t there. But by going in totally silent about it, and allowing people to be like ‘Wait, what is this. This isn’t making sense.’ And then for it to make sense in the end. That’s the best way to experience it. I was pretty stoked that they kept it under wraps.”

“You got to do this stuff in the ’80s, ya know.”

Made on a reported budget of around $50 million, Underwater is indeed the very definition of the sort of movie that “doesn’t usually get made” these days, and though the risk may not have entirely paid off at the box office, the fact that an original, big-budget Hollywood creature feature was even released in the year 2020 is something of a gift. Especially to fans of Lovecraft, whose ticket purchase gave them the coolest representation of Cthulhu that has ever graced the big screen. That it was a surprise, well, that was just the icing on the cake.

You can see more creature concept art, including those early squid-like designs Eubank touched upon in our chat, by picking up Underwater on Digital HD and Blu-ray today.