At every opportunity, Marvel Studios boss and producer Kevin Feige refers to the end of Phase 3 - which concludes with the untitled Avengers 4 - as the "culmination" of the Marvel Cinematic Universe. The long-form story that begin with 2008's Iron Man and that changed Hollywood's thinking about movie franchises, is coming to an end. At least in its current form.

All of the major plots of the 20+ films - and virtually every character in the franchise - leading into Avengers 4 will factor into the next two Avengers movies being directed by Anthony and Joe Russo (Captain America: The Winter Soldier, Captain America: Civil War), but what does "culmination" really mean given that we know there are more sequels coming, featuring many returning characters?

Related: Why Phase 3 Needs To End MCU As We Know It

It seems like Phase 4 is still happening and will be capped off by some massive team-up, whether that be Avengers 5 or Avengers 6 so on the set of Avengers: Infinity War we asked the Russos directly. It was our last question in our second group interview with the brother-directors and their analogy is the best we've heard yet.

The work "culmination" keeps getting used. And even when we spoke with Kevin Feige about Guardians of the Galaxy Vol. 2, he said after 2019 everything is going to look different. Without spoiling anything - What does that mean to you?

Anthony: I think as storytellers what it means for us is that while you're always looking for cataclysmic events in a film, to change a character to challenge a character, and to sort of explore who that character is and test who that character is, it gave all of us in this film an opportunity to figure out, well, what were those ultimate tests for these characters, you know what I mean? To sort of go one step further even than how you would normally test the character in one of these films because we had the freedom to sort of think of it in many many cases as sort of a final test.

Joe: If you were to think of the Marvel universe over the last ten years of the book, this is the ending of the book. And then there may be new books written, but this is certainly the ending of this book.

The stakes will be higher than ever, and with the most dangerous villain yet needing to prove himself to audiences - especially given the notably lack of worthy villains on the overall MCU. There will be death. Some actor contracts are coming to a close and as Marvel Studios keeps pushing to evolve and keep things fresh, that means Phase 3 needs to end the way they're doing things, opening up even more opportunities for new characters and new teams of them exploring new locations and stories.

More: Will MCU Still Have ‘Phases’ After Avengers 4?