He said: "You know, we've had trilogies before, but I was thinking, why does this feel so different and so much of a passage of some sort? And it's because Guardians really was the first movie that was completely outside of the realm - it tied in with Thanos and Infinity Stones, but The Avengers weren't in it, and we weren't setting up Tony Stark's next adventure, or Captain America.
"It was really our attempt of saying, we don't want to just do superhero movies. We wanted to do a big space movie and it worked in a crazy way, entirely because of James Gunn.
"So, it just feels like this trilogy, and James writing and directing all three of them, represents something unique within the pantheon of the MCU that I'm very proud of."
The emotional conclusion to James Gunn's trilogy sees the Guardians teaming up to protect Rocket, who has been left seriously injured after a kidnapping gone awry. The team discover that he was created by an evil scientist known as The High Evolutionary (Chukwudi Iwuji) many years before, who is now planning on kidnapping him back to retrieve the data chip embedded into his body.
On top of all of this, Peter Quill is having a rough time of it; after Gamora died elsewhere in the MCU, he's still getting to grips with the alternate-past version of her who survived, and absolutely hates him.
Star Chris Pratt states that the character's emotional journey this time around is defined by how "lost" he has become without that relationship.
He said: "There's a wonderful monologue that Dave Bautista gives about how Quill is a guy who needs to learn how to swim. He's been hopping from lily pad to lily pad, woman to woman, and relationship to relationship.
"I think, oftentimes, we find ourselves in our relationships or in the affiliations we have with a team or a family, whereas he has been lost. In the beginning, he was running away from the death of his mother, but he got to pretend to be this character based on these pop culture icons of his childhood of the late-'80s; he was dancing around, but it was B.S., you know?
"He's a guy who's constantly been searching for who he is, and then he found it again in his relationship with Gamora. And so, when that's stripped away from him, he's a guy who's realising that all of these various people that he's found that are Quill, none of them have been the real him."
Everybody on set was emotional at saying goodbye to their characters, but Pratt took a different approach, reasserting to everybody that this was a celebration: the culmination of nearly a decade on our screens.
"The thing that you want to avoid is regret", he continued. "One day, looking back and thinking "why did I just let that go by without trying to enjoy every moment? Why didn’t I savor that?" And I knew that going into this movie.
"The feelings that I was writing down in the back of my mind about the experience were ones of gratitude to James, and so I wanted to be the guy who reminded everyone how far we’d come, and all the things that we’d overcome. And so, I read a few reviews from people who had said that Guardians was going to be the first big Marvel flop - I don’t know how those ended up in my notes for the past nine years!
"I have the experience of being part of things that have come and gone. I remember on Parks and Rec, it felt like the last day of school before summer at the end of seven years, and you’re not going to be coming back to school together.
"It’s that summer camp vibe of wondering "Am I ever going to see these people again?" And having gone through that before, it was important that I be present but also that I coerce other people into being present as well, that was a responsibility I felt I had."
On the other side of the camera, Gunn is preparing to wave goodbye to the world of Marvel as he settles into his new role over at DC, with preparation for his Superman reboot underway.
He said: "I'm going to miss these characters, that's the saddest part for me; I really, truly love all of them. I'm going to see all these people again, they're all friends of mine, but I'm not going to see the characters.
"I won't be writing these characters again, at least not in the near future, so, that's a real sadness."
However, there was one crucial component that kept his spirits high whilst making the movie: putting together one last Awesome Mixtape for Peter Quill. Knowing that this was his final chance to include as many of his favourite artists as he could, Gunn realised he had a bigger responsibility than before when it came to compiling the eclectic soundtrack.
"It has become a strange process because the first two albums were huge hits", he continued. "They changed the lives of some of these artists who now have big hit songs, and so, I know that when I’m choosing a song, it’s going to be something that a lot of people listen to.
"I want to give good music to people by good bands, and I snuck in a couple of my favourites; my friends The Replacements are in there, as well as my hero Alice Cooper. When I’m writing, I write the music into the script, but it was very difficult choosing the music for this movie because in the first two movies, they were basically all ‘70s pop hits.
"Yondu gives Peter Quill a Zune at the end of the second movie, and so now it's music from the ‘70s, ‘80s, ‘90s, 2000s, I could choose from anything. It’s like at the end of The Hurt Locker, with him looking at all the stuff on the shelves and not knowing how to make this choice - it was very difficult to choose the music because of that.
"There’s songs that I have on lists that I could never use. Cruel to Be Kind by Nick Lowe has been on every list that I’ve had for the movies I've made, and I’ve just never found a place to work it in."
So, as Gunn says goodbye to Marvel, we can at least rest assured: there will be plenty more classic rock to come as he makes DC his home.
Guardians Of The Galaxy Vol. 3 is released in UK cinemas on Wednesday, 3rd May.Shop our Guardians of the Galaxy merch.
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