Filmmaker Allan Ungar and Firefly star Nathan Fillion were just a couple of Uncharted fans tired of waiting for Hollywood to bring the action-adventure videogame to the big screen. And while Stranger Things producer Shawn Levy and Spider-Man: Homecoming star Tom Holland have been linked to an official Uncharted movie from Sony, that project has hit some snags over the years. So Ungar and Fillion decided to make their own project in secret this summer, and on Monday the duo debuted a 15-minute live-action “fan film.”

For years, gamers have been dream-casting Fillion as Nathan Drake, the thrill-seeking tomb raider of the Uncharted franchise. This became reality (albeit unofficially) in a story centered on the lost treasure of the Flor de la Mar ship. Stephen Lang of Avatar portrays Nathan’s old friend and mentor Sully, Episodes’ Mircea Monroe pops in as Nathan’s wife, Elena, and the cast is rounded out by Geno Segers and Ernie Reyes Jr.

Now what seemed like a one-and-done passion project could become something more. Ungar tells EW he has already received “a couple emails” about “what this could mean as a digital series or something further.” So keep your fingers crossed. “I think if it makes sense and if it’s done right, I’d be thrilled to have a conversation about it and possibly see this specific story continue,” he says. (Sony had no official comment to make at this time about Ungar and Fillion’s short, or the status of its Uncharted movie.)

Ungar and Fillion spoke with EW over the phone to discuss how they secretly shot the short over one week in May, using the games as inspiration, and Uncharted game developer Naughty Dog’s response to it.

ENTERTAINMENT WEEKLY: Your fan film was quite the surprise. How long had you guys been sitting on this project?

ALLAN UNGAR: January.

NATHAN FILLION: Yeah. January is when we started plotting it. And May? Did we shoot it in May?

UNGAR: Yeah. First week of May we shot it in L.A., but we agreed to do it in the last couple days in January.

Whose idea was it to make a short film like this?

UNGAR: The idea had come to me a couple years ago. It was shortly after the “Power/Rangers” short had come out and there was this period of time when we were seeing an influx of these fan trailers and fan films that had filmmakers and actors coming together to give back to the fans. It had taken a long time for both of our schedules to work out, and our mutual friend Alex Lebovici put us in touch in January. I was in Los Angeles for some meetings, and Nate and I sat down for dinner to, really, pitch him this idea that I had for the last several years, and we just took it from there.… I did say to Nathan, “Listen, I’m not proceeding with this if you are not interested whatsoever. Obviously, it’s not to pressure you, I just want you to know that the reason I’m doing it is because I believe in what it represents and what it could be, and I don’t think there is a point in trying to go outside the system and make a fan film if it’s not gonna be with you in that role.”

FILLION: Aww!

Can you walk me through assembling the team? It was also a surprise to see someone like Stephen Lang involved with this project.

FILLION: Right?! That was so cool.

UNGAR: Yeah, it’s funny. Bruce Campbell emailed me today to say he thought it was great. And it’s funny because everyone’s saying, “Hey, what about Bruce Campbell [to play Sully]?” So he was really happy that it was Stephen Lang. We have to call him Slang ’cause he’ll get upset. Once he hit 60, he decided he was getting a one-name title. Slang and I had been friends for a few years. We worked on a film together called Gridlocked a few years ago, and his sons are huge fans of the [Uncharted] franchise. I had popped one of them a note and said, “Hey, what do you think? I’m gonna ask your pops if he might be interested in this.” And they were like, “Oh my God! Please, this would be incredible.” At that point it was just Nathan and myself and our little team that decided to do this. And so I called Slang up, I said, “It would mean the world to me if you would come on this full adventure with us,” and he was happy to oblige. He had a great time.

You mentioned the “Power/Rangers” short that came out a while back. There was that whole pushback from Saban where the video got pulled for being unofficial, and then reissued. Was there a concern that releasing a project like this would have the same outcome?

UNGAR: We weren’t worried because, given the material and us being very clear and straight up about what we were trying to do, there wasn’t much of a concern. And actually [Naughty Dog Vice President] Neil Druckmann, the director of the last couple games, had tweeted about it today. He loved it.

Obviously, you guys shot this outdoors in L.A. Was it difficult to keep this shoot a secret for as long as you did?

UNGAR: Yes and no. Nathan, what do you think? It wasn’t that difficult.

FILLION: We gave it a different name, so the crew didn’t know what they were working on when they signed on. And then as soon as you arrive in costume and they see what’s happening, everybody got very, very excited. Everybody felt like they were on the inside of something super-cool, and no one wanted to blow it.

UNGAR: I think there was one instance where one of the people on the camera team was so excited about the Superman jump where we had you on the crane, they posted an Instagram Story and tried to erase your face. One of the producers caught it and was like, “No, no, no, no, no! You gotta take that down.” And I’ll never forget the set medic we had on the day for Nathan’s big fight scene in the house. Like Nathan said, nobody knew what they were working on. The movie’s codename was “Breaking and Entering.” It was a short film, nobody thought anything of it. And the set medic showed up and asked somebody, “I gotta clarify this: Fillion’s here and he’s dressed like Nathan Drake. Is this what I think it is?” It just went from there. People were just geeking out.

That fight sequence was pretty badass. I was noticing even the hand-to-hand combat was very similar to Nathan Drake in the game. Did you guys pore over gameplay footage? How did you go about choreographing that?

UNGAR: Joe Perez, the stunt coordinator, who I’ve known for 10 years, helped me out on the very first short film I made when I was a teenager in school in L.A. I put him up for some other films over the past couple years and I asked him as a favor to come do this, and he’s obsessed with the games. What we did was, I created a reel from YouTube from clips from the game of certain moves to convey the way Drake moves, because he’s not a trained fighter. He’s taught to survive, he’s a brawler, he’s dirty, he’s messy, he’s not graceful. I had told Joe what I wanted to see, and I roughed out how I envisioned the fight and told him what gaps to fill in. Almost everything Nathan does in that fight is seen in one of the four games.

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Did you guys end up shooting additional footage that you couldn’t fit in for whatever reason?

UNGAR: Nathan is obviously a funny guy, so he had some alternate lines in the scene. I think we’re probably going to release a blooper reel and some of those extended moments. But no. We set out to make this 15 minutes, and we kept it in that timeframe.

FILLION: We filmed a little teaser, a commercial of sorts — the shoulder holster hanging over the chair of the desk in the office. The lighting was so gorgeous; the desk, the set was amazing. Just the shoulder holster hanging there, a slow push in on it, and then you don’t see who, but someone comes in and takes the holster and goes away. We thought we would use that for a tease of some sort, but our first cryptic hint out to the fans was picked so immediately we didn’t need to hit it over the head.

UNGAR: We didn’t have to try harder.

Nathan, what was your first introduction to the game?

FILLION: I’m just gonna say I fell in love with the game like everybody else in 2007. That’s all I got right now. I have more story for that. It’ll come out at another time.

I was falling down a rabbit hole on Tumblr, and it very much seems like fans of the game have been dream-casting you, Nathan, as Nathan Drake for years. Now that we actually have a feature film in the works, was there ever a point where you were in discussions for that film? Did anybody approach you about anything Uncharted-related? Aside from Allan, of course.

FILLION: Nope. No one approached me, I never auditioned for any role, I’ve never been in any talks for any role. I think it’s fair to say Allan and I, along with everyone else, just got tired of waiting. We just wanted to see something. And I’m very excited to see what Sony is coming up with. I’m a huge Tom Holland fan. I think that kid’s on fire. He’s the best Spider-Man we’ve ever seen — that’s a fact. He’s just got the heart that the part needs. I’m just excited to see what they come up with. I think we just got tired of waiting.

Allan, can you talk a bit about developing this particular story?

UNGAR: Everybody wakes up in the morning with their routines. Some people check the stock market, I check the trades in the movie business and I look at the videogame stuff. When the [Uncharted franchise was] somewhere around the second game — so sometime in 2009 — they used to run polls on big videogame websites and they used to say to people, “What would you like to see in the next outing?” There was always a really great list of real-life mystical cities and hidden treasures that hadn’t been explored. The Flor de la Mar, I found, was a very fascinating story, and it wasn’t until I had come back to this idea in January that I settled on that. Jesse Wheeler, who co-wrote this with me, we did a lot of extensive research. We were pretty fascinated with regards to the historical figures that were crossing paths at this time in history when the Flor de la Mar sank, and I just thought it would make a killer conspiracy in the vein of Indiana Jones and National Treasure, taking something that’s real and adding some mystery and fiction around it.

Do you guys have any other plans at this point to do something else Uncharted-related?

UNGAR: I think that we’re very happy and we’re very proud of what we accomplished, and if it lives and dies as a fan film, that’s great. If Sony… I actually got a couple emails today, I’m not gonna say from who, but there’s definitely people talking about what this could mean as a digital series or something further. Obviously there’s interest in there, and I think if it makes sense and if it’s done right, I’d be thrilled to have a conversation about it and possibly see this specific story continue.

I know I’m not the first person to note the similarity between Sam Drake [Nathan Drake’s brother in Uncharted 4] and Luke Perry. So if you guys could make that happen, that’d be awesome.

UNGAR: [Laughs] Yeah. I thought that way when I played the fourth one.