*Caution: Spoilers Ahead! Seriously, if you haven't seen Solo: A Star Wars Story yet and you don't want some major reveals totally spoiled, don't keep reading. Not even a little bit.**
When Alden Ehrenreich stepped into the iconic shoes of Han Solo for the action-packed Solo: A Star Wars Story, the young actor knew he was going to be under a lot of pressure, and would be joining a movie universe bigger than arguably any other fandom in film history.
What he didn't know, it turns out, was who, exactly, would be showing up at the end of the film for a mind-blowing twist that also proved to be one of the movie's most surprising cameos.
At the end of Solo, it is revealed that Emilia Clarke's character, Qi'ra, has secretly been working for one of the Star Wars franchise's most iconic villains -- Darth Maul.
According to Ehrenreich, he only found out about Maul's inclusion in the film when they were "going back and doing a few pick-up [shots]."
"There was a part in the script where it said 'somebody appears' and it wouldn't say who," the 28-year-old star recently told ET's Ash Crossan at a Los Angeles screening of his new war drama The Yellow Birds. "So there was a lot of speculation amongst the crew and cast about 'who is that going to be?' and then I found out like a few months ago."
In the film -- which is set around a decade before the events of the original Star Wars: A New Hope -- the red-face, horned villain returns, having survived his seemingly fatal confrontation with Qui-Gon Jinn (Liam Neeson) in Star Wars: Episode I - The Phantom Menace.
Fans who watched the two animated Star Wars series, The Clone Wars and Rebels, already knew of Maul's survival and life after being cut in half, but his existence alone was a huge surprise to all fans as his involvement was kept a closely guarded secret during production and following the movie's release.
Original star Ray Park reprised the role as well, giving it a surprising and exciting continuity.
Given the vast potential for future Han Solo standalone projects, Maul's involvement begs the question of whether or not the charming smuggler will ever get to face off against the big baddie in a follow-up film.
Even though Ehrenreich says he doesn't know for sure, he admitted, "That'd be pretty cool."
As for possible sequels, the star said he'd love to just see how all the interpersonal connections between the characters might develop during the span of time not seen in the other films.
"I think all the relationships, between me and Lando [Calrissian], me and Qi'ra, all those relationships are so dynamic and fun and interesting, I'd love to see how those play out," he shared.
While his life-and-death adventures in Solo were crafted with the adventurous, tongue-in-cheek spirit of the beloved sci-fi franchise, his role in the gritty Iraq War drama The Yellow Birdswas a vastly different experience.
In the film, Ehrenreich stars as a soldier named Brandon Bartle who forges a friendship with fellow soldier Daniel Murphy (Tye Sheridan), and faces the horror, confusion and desperation of war.
"Think one of the big takeaways I learned is that unless you actually live the actual thing you kind of have no idea," Ehrenreich said of his experience playing a soldier. "We actors did the best job that we could and spent a lot of time trying to understand these people but the element of actually having somebody trying to kill you is not something I think any of us could actually wrap our heads around."
The actor said that playing that sort of role gave him and his co-stars a "deeper sense of gratitude for the people who put themselves in those situations."
The Yellow Birds is now playing on DIRECTV, and in select theaters and on-demand June 15. Solo: A Star Wars Storyis playing in theaters everywhere.
Maul's appearance at the end of Solo mirrors the unexpected and mind-blowing cameo made by Darth Vader at the end of the Star Wars franchise's previous standalone film, Rogue One.
ET spoke with Rogue One star Riz Ahmed last year, and the actor admitted that the shocking appearance was a surprise even for the cast.
"They kept that from us! That was never in the script. We didn't know about it!" Ahmed said, explaining that she first found out about Vader's epic battle when the cast screened the movie for the first time at Skywalker Ranch before its release.
"It was the first time we saw it, so it was like, 'Oh okay, the film's finished... Darth Vader? Epilogue? Uh... What is going on here?' And we just all started shouting, and cheering and clapping in a screening room," he recalled. Check out the video below to hear more.
'Solo: A Star Wars Story' Screenwriters Tackle 'Fan Service' and the Kessel Run (Exclusive)
Emilia Clarke Ignored Her Family’s ‘Star Wars’ Screening to Watch the Royal Wedding
'Solo: A Star Wars Story' Review: Prepare for an Unexpectedly Bold Adventure