The following potentially contains spoilers for Avengers: Endgame**, but will not reveal specific information.**
For a major blockbuster tentpole movie like Avengers: Endgame, there's nothing worse than spoilers. If people know what happens in a movie they may be less inclined to go see it, and fans prefer to be surprised, and so those spoilers are guarded like nothing else. Marvel even goes so far as to create fake scripts to prevent the truth from leaking out, and it seems that Sebastian Stan got taken in by that.
The actor, who plays Bucky Barnes, The Winter Soldier, in the Marvel Cinematic Universe, recently appeared on The Tonight Show Starring Jimmy Fallon and he admitted that for one key scene that he was in, he was told the scene was something completely other than what it actually was. According to Stan...
I was told it was a wedding, that there was a wedding we were filming. And I was like, ‘Who’s getting married?’ But everybody was dressed very formal, and I was looking around, and then two people weren’t there. So I guess that was the bride and the groom.
If you've seen Avengers: Endgame, then you know exactly what Sebastian Stan is referring to here. If you haven't, then it only needs to be said the movie contains a scene where several MCU characters are dressed formally for an event. While Sebastian Stan was told his character was attending a wedding, that's not actually what's happening.
Sebastian Stan himself admits he thought the idea of a wedding seemed odd, he had no clue who would be getting married, but it seems it wasn't until later, possibly even the first time he saw the movie, that he realized that wasn't the case.
It shows to just what an extent Marvel Studios and the Russo Brothers were going to make sure everything in the film remained secret. Sebastian Stan doesn't have the reputation of a Tom Holland or a Mark Ruffalo. He's not known for giving away the game. And yet, he wasn't trusted with the truth of the scene. He wasn't even told the general information of the event that was actually taking place, nevermind the specifics.
One assumes that several other people in the same scene are standing there thinking they're at a wedding. It's one thing to not really know what you're doing when you're part of a major green screen CGI battle, but there are no digital effects at this moment. It's just a shot of people standing around, and yet the actors on screen are as clueless as to what the reality is as when they're fighting Thanos by looking at a tennis ball on a stick.
Check out Sebastian Stan's full comments on The Tonight Show in the clip below.
Of course, now that Sebastian Stan has seen the movie, he could spoil things, but he's being careful not to do so. The gloves may be coming off soon, however. The Russo Brothers say that after two weekends of a movie's release, spoilers become fair game, so if you still haven't seen Avengers: Endgame after this weekend, you may need to start being extra careful.