Robert Downey Jr.’s Tony Stark took a piece of many fans’ hearts when he debuted as the superhero over a decade ago in 2008’s Iron Man. The film began the Marvel Cinematic Universe and introduced us to a now-iconic character. The 54-year-old actor’s portrayal incorporated parts of himself; he even improvised some of his most famous lines. Avengers: Endgame, which marked Downey's final MCU film, was no different, and now we’re learning of another part of the film that came straight from the actor.

Earlier, fans discovered that the heartfelt line, “I love you 3000,” from Iron Man in the final Avengers film was inspired by Downey’s own children: the actor altered it to match what his kids say to him in real life. And that wasn’t the only bit of improvisation in the blockbuster film. According to co-director Anthony Russo, Downey added the part in which Tony Stark calls Steve Rogers a liar.

In Endgame, Iron Man returns to Earth and reunites with Captain America, who he hasn’t seen since the events of Captain America: Civil War. The scene is already tense when Tony confronts him and says, “No trust, liar.” As reported by CinemaBlend, Russo revealed to Empire that the word “liar” was Downey’s choice. He explained:

“I think that was one of Downey's most inspired performance moments in the movie. He very much reverts to—this is the guy who felt forsaken by his father. You can see his intimacy and trust issues in that moment when he turns on Cap. Downey performed the scene with a lot of energy. We didn't do it many times, because he was expending himself so, so much. He understood it very well.”

Some of the most emotional scenes throughout the MCU have been improvised by the actors, such as Tom Holland adding his own bit of dialogue as he faded away in Avengers: Infinity War. It goes to show that the stars behind our favorite superheroes are just as invested as we are—and that sparks better results in the end.