In its three-hour long runtime, Avengers: Endgame finally brought all of the superheroes from the Marvel Cinematic Universe together, many of them sharing the screen together for the very first time. But many fans were clamoring for one reunion that never took place, even though it had to happen at some point in the MCU's history.

Avengers: Endgame writers Christopher Markus and Stephen McFeely started their Marvel Studios journey with Captain America: The First Avenger, in which they pitted Steve Rogers against his greatest foe the Red Skull. So with Red Skull playing a role in both Endgame and Avengers: Infinity War, why didn't the two interact? It turns out, that was a part of the early plan for film.

The two writers spoke at San Diego Comic-Con 2019, revealing that they initially had a manifesto for the film that featured Captain America going into space and traveling to Vormir to get the Soul Stone.

"In the manifesto document, there was one theory that [it was] Cap who goes to space, and he has to collaborate with Red Skull to get the Stone," Markus said.

Even though fans were deprived of this reunion, the movie probably turned out better as it was; the Vormir scene provided an emotional moment between Black Widow and Hawkeye, with the former sacrificing herself in order to save those who were lost in Infinity War.

But the writers, who have penned all of the Captain America trilogy and the last two Avengers movies, knew that they had a plan for Red Skull when he was blasted by the energy of the Tesseract in Captain America: The First Avenger.

"We did send him to space and send him away very much on purpose," Markus said, and it just happened to work out when they were figuring out what to do with the Soul Stone in the Avengers movies.

But at the end of Avengers: Endgame, Cap had to go back in time to deliver the Infinity Stones to their rightful place in history — which means he would have had to reunited with the Red Skull at some point. Perhaps that's a story that Marvel Studios will tell another day.

Avengers: Endgame will be available on Digital HD on July 30th, followed by its Blu-ray and DVD release on August 13th.