Actress Katherine Langford had to be cut from Avengers: Endgame because her role as an older version of Iron Man's daughter fell flat with test audiences.

The 13 Reasons Why star was reported to have been tapped for a secret role in the new Marvel blockbuster last year (18), but when the Avengers: Infinity War sequel opened in theatres last month (Apr19), she was no longer part of the line-up.

Directors Anthony and Joe Russo have since opened up about the reason for her axe from the movie, revealing Langford had been cast as an older version of Morgan Stark, the daughter of Robert Downey, Jr.'s character Tony Stark/Iron Man, and was featured in a dream sequence as the superhero faced his death.

The scene would have been similar to one between the villain, Thanos, and his 'adopted' daughter Gamora, played by Josh Brolin and Zoe Sandana, in the previous film.

"There was an idea that Tony was going to go into the metaphysical way station (dream-like state) that Thanos goes in when he snapped his fingers (in Infinity War), and there was going to be a future version of his daughter in that way station," Joe explained on MTV's Happy Sad Confused podcast.

However, the 23 year old's scenes just didn't work and had to be cut during post-production: "We showed it to a test audience and it was really confusing for them," he added.

His brother and co-director Anthony Russo continued, "We didn't feel an emotional association with the adult version of his daughter. It wasn't ringing to us. It wasn't resonating to us on an emotional level is why we moved away from it (sic)."

The thought process behind the sequence was to have Tony's daughter forgive him for sacrificing himself to save others, but, Joe shares, "It just was too many ideas in an overcomplicated movie."

Langford has yet to offer up her thoughts on her cancelled appearance.