The 39-year-old actor, who stars as Peter Quill / Star-Lord in the Marvel Cinematic Universe, took to Instagram on Monday to share footage from the set that he secretly snapped on his cell phone.
[Warning -- slight spoilers for Avengers: Endgame in the video below.]
"I remember being blown away in this moment on the @avengers set," Pratt captioned the video, which includes co-stars Chris Evans, Mark Ruffalo, Chris Hemsworth and more rehearsing a scene. "Nobody was allowed to film anything on their phones. I said screw it."
"No rule was going to stop me from seizing this once-in-a-lifetime opportunity to capture this collection of stars, a group that likely will never be in the same room again," he continued. "We are so blessed."
Fans were quick to comment on the video, including celebrities like Vin Diesel, who wrote, "And that's why you are STAR-LORD!! Hahahaha. All love..."
"I'm calling the cops," Diplo added.
Pratt also shared a selfie from set with Karen Gillan (Nebula), raving over the film's massively successful opening weekend in the caption. "Just really can't believe how well @Avengers is doing. And how good it is," he wrote. "I'm floored by all of it. I did the math... at about $12 per ticket, and a $1.2Billion opening that's ONE HUNDRED MILLION PEOPLE who watched the movie in one weekend. I think."
ET caught up with Pratt on the red carpet at the Avengers: Endgame premiere in Los Angeles earlier this month, where he revealed that his 6-year-old son, whom he shares with ex-wife Anna Faris, has a favorite Avenger... but it's not Star-Lord!
"I'm, like, Jack's fourth favorite Avenger," Pratt joked. "Well, actually, now that there's even more Avengers, I think I'm, like, ninth favorite."
"He loves Spider-Man [Tom Holland]. He's a big Spider-Man fan," the proud dad added. "He loves Captain America [Chris Evans], he loves Black Panther [Chadwick Boseman]. He loves them all."