Captain America: Civil War included the revelation that The Winter Soldier was responsible for the murder of Howard and Maria Stark. Thanks to the manipulations of Baron Zemo, the movie ended with Steve Rogers and Bucky fighting Iron Man, and the former HYDRA assassin would get his arm blown off in the process.
As you may recall, Bucky at one point attempted to tear the arc reactor from Iron Man's chest, an idea first explored by Marvel Studios Head of Visual Development, Ryan Meinerding.
This is an incredible piece of artwork, and there's not been a more personal battle in the Marvel Cinematic Universe since the 2016 movie was released. Steve and Tony Stark would eventually put their differences aside in Avengers: Endgame, and Bucky will continue searching for redemption for his past actions in upcoming Disney+ TV series The Falcon and The Winter Soldier.
We'll have to wait and see how that goes, but with Iron Man dead and gone, Bucky definitely has the opportunity to step out of the shadows and becoming a hero like his best friend before him.n
Check out the concept art below: