Going into Avengers: Endgame, 21 movies within the Marvel Cinematic Universe will tie together their narrative threads for the ultimate culmination in big screen story telling. Some films will be more crucial to the narrative of Avengers: Endgame than others, leaving many fans guessing which they should re-watch or watch for the first time prior to seeing the upcoming movie. Now, directors Anthony Russo and Joe Russo have revealing which movies will be the most integral for the ultimate viewing experience.

"[Captain America:] Civil War and [Avengers:] Infinity War without question because the events of Civil War directly affected Infinity War, and we would argue that the reason they lost to Thanos is because of Civil War," Joe Russo said in the interview featured in the video above. "Clearly, that carries over to Endgame. If you're going to add one more in there, I'd probably say [Captain America: The] Winter Soldier, only in that those are the four movies we directed, and they're all thematically connected to one another."

Captain America: The Winter Soldier was the first Marvel Studios production with the Russo Brothers worked on, releasing back in 2014. "This is from our point of view in the storytelling," Anthony Russo said. "This is the thread we're working with."

Still, fans should probably check out the first Avengers movie from 2012 and its 2015 sequel in Avengers: Age of Ultron. While many suspect the Ant-Man movies will be integral due to expectations of the Quantum Realm, it seems unnecessary given that Scott Lang is the only hero with knowledge of the subatomic world. This means he will have to provide an explanation of the Quantum Realm to the other heroes which will likely get the audience up to speed, similar to how Wong and Doctor Strange explained the Infinity Stones at the beginning of Avengers: Infinity War.

"Here's the thing: you cannot chase bigger with movies," Joe Russo said of his approach to Avengers: Endgame. "All you can do is chase storytelling. So, Endgame is us committing to storytelling on the highest level. We poured our heart and soul into this one, and we'll see how audiences respond to it."

Heading into the film, the Russo Brothers locked in a running time of more than three hours. Still, they fit each narrative beat into the lengthy constraint. "That was very much worked out on the script level with [Christopher] Markus and [Stephen] McFeely," Anthony Russo said. "We spent a long time with them exploring all the possibilities and honing down on what the essential storytelling was. That's such a complex question. You can't really be dealing with that once you get to production. That's definitely a script issue."

Which movies are you watching or re-watching before Avengers: Endgame? Let me know on Twitter, @BrandonDavisBD!

Avengers: Endgame opens in theaters on April 26.