About five years ago, Marvel Studios President Kevin Feige found himself plotting the future for the wild, experimental "cinematic universe" that he helped start in 2008. He wanted to do something that isn't done in blockbuster tentpole series. He wanted to come up with an ending for the Avengers saga.

Ending "is not a scary word," Feige said. "It's a necessary word."

So necessary, in fact, that it's part of the title of "Avengers: Endgame," which opened Thursday evening.

Endings are a rarity in the franchise moviemaking business; especially when one's popularity has only multiplied as the movies of Marvel have. But Marvel Studios, which has never shied away from a little rule-breaking, is taking a sledgehammer to that old "don't leave money on the table" maxim.

What exactly that means for the future of the Marvel Cinematic Universe (MCU) is something of a state secret. Feige said that it will be "definitive," though.

"For us that means bringing to a conclusion the first three phases, the first 22 films in the MCU, so that everything thereafter is a new start," he said.

So "new," in fact, that Feige won't even discuss what's to come beyond the July release of "Spider-Man: Far From Home." That includes refusing to confirm reportedly in-the-works projects such as the "Black Widow" stand-alone, "The Eternals" or "Shang-Chi," or talk about plans for the 20th Century Fox properties such as "Deadpool" and "X-Men" that are now under his purview.

They have the next five years mapped out; they're just not letting audiences peek behind the curtain — at least until the end of "Endgame."

"How we leave 'Endgame' will help define where we're going for many people," Feige said.

Cast felt nostalgic

Filming the movie proved an emotional experience for many of the actors, several of whom have been working together for almost a decade.

"I was pretty teary-eyed," said Chris Evans, who plays Captain America. "This is the culmination of a really long endeavor. It kind of wraps up the journey for a lot of these characters."

It led to a lot of reflection, about where they started and how they've grown. Scarlett Johansson (Black Widow) noted that she'd been developing her character for 10 years and is excited that the role has evolved from a "sexy secretary" type to a more fully realized woman.

"The whole shoot felt pretty nostalgic," added Chris Hemsworth (Thor). "We were constantly talking about when it all started to how we pulled this off and what we were a part of."

But he also admits he was "kind of happy to get off the set." An eight-month shoot can wear even on someone with superpowers.

Everyone agrees that the shoot was grueling.

The directors, who also helmed "Winter Soldier," "Civil War" and "Infinity War," said it was the hardest of their lives.

"This went far beyond anything we'd ever done before," said Anthony Russo. "There's a reason why movies aren't made this way normally."

A different approach

At the same time, the fact that this was unconventional was also one of the draws for the filmmaking brothers.

"I think the only reason we stuck around is because they were committed to an ending and we're deconstructionists," said Joe Russo. "We like to take things apart and see the ramifications of what happens. [In] 'Winter Soldier' the good guys became the bad guys, 'Civil War,' we divorced the heroes, 'Infinity War,' we killed half of them. We like to smash it and look at how you can put the pieces back together."

And no one, not even Feige, regrets putting the MCU on this one-way path.

That's not to say he never second-guesses himself, however. He spent part of the run-up to the movie's opening worrying about how Avengers fans would react.

"That ending was one of the reasons why we wanted to make the movie," Feige said. "That's how we sold it to Disney. We were confident in it. But then a week or two weeks before the film came out, I went, 'Oh, no. We're killing all these people. What if the audience totally rejects it?' "

He's been in this spot before. The release of a movie often is accompanied by a wave of insecurity.

"When you can't touch it anymore, you go, 'Wait a minute: Should we have touched it more?' " he said.