Mark Ruffalo spoiled Avengers: Endgame during an interview a few weeks ago. Marvel Studios, the Russo Brothers, and all of the actors from the movie went to great lengths to keep everything under wraps, but Ruffalo has continued his streak and has solidified his reputation as the MCU's worst spoiler. He has even surpassed Tom Holland, but that might only be due to the fact the Peter Parker actor hasn't been doing press for Endgame. There are MAJOR SPOILERS for Avengers: Endgame below, so read ahead at your own risk.
Back at the beginning of April, Mark Ruffalo, Chris Evans, and Karen Gillan all sat down for an interview. Ruffalo's reputation is well-known in the Marvel Cinematic Universe and Evans even called him out for it in the interview in a playful manner. However, even talking about spoilers led directly to the Hulk/Bruce Banner actor spoiling Avengers: Endgame after all. You can read what Ruffalo had to say below.
"I didn't even get a whole script of this movie. I don't know why. The script I did get had dummy scenes in it. He (pointing to Evans) gets married in this!"
As we all know from watching Avengers: Endgame, Steve Rogers ends up going back in time to live the rest of his life with the love of his life, Peggy Carter. He only seconds later (due to the Quantum Realm) appears as an old man with a wedding ring on. Rogers and Carter are seen getting their dance by the end of the movie and Mark Ruffalo spoiled it weeks ago, which many fans thought of immediately since the camera, which was set on the three actors does an awkward closeup on Ruffalo's face, hid Evans' reaction.
In fairness to Mark Ruffalo, he may not have really known about Steve Rogers getting married in Avengers: Endgame since he admits he was given dummy scripts with fake scenes. However, it looks like the Russo Brothers may have goofed this one up by leaving something real in it. Whatever the case may be, Ruffalo probably learned about the Steve Rogers ending while watching the world premiere earlier this week with the rest of those in attendance. This may have actually been a genuine mistake, but it certainly seems very on brand for the actor.
Mark Ruffalo tends to get a bit excited when talking about the MCU, which leads to him accidentally leaking some secrets to the fans. He famously broadcast the first 10 minutes of audio from Thor: Ragnarok during the world premiere and spoiled the end of Infinity War nearly a year before the movie came out, much to the horror of Don Cheadle who was sitting right next to him during the interview. Cheadle says he refuses to do press with Ruffalo for that very reason. You can watch the interview below, thanks to the E! YouTube channel.