Guardians of the Galaxy
The Guardians of the Galaxy on a poster for Vol 2. Marvel Studios

James Gunn who wrote and directed both of Marvel's hugely successful Guardians of the Galaxy films, has been discussing how work on the announced trilogy-concluding sequel is coming along.

Speaking to Collider ahead of the film's home release on DVD, Blu-Ray and digital services, Gunn also talked about when the sci-fi adventure will start filming and revealed that he knows roughly when it will be released.

Guardians of the Galaxy Vol 3 was announced earlier this year ahead of the release of Vol 2, which proved a box office smash taking even more money than the 2014 original.

Gunn says Vol 3 will start filming in "a little more than a year" before revealing that he knows basically when the film will be released. The timing of production would suggest a release date in early 2020, either the February/March or May time slots Marvel likes to occupy.

Asked about the writing process for the film, Gunn said: "The truth is, the first movie is the first act, the second movie is the second act, the third movie is the third act.

"So I'm tying a lot of stuff together in the third film, we get a lot of answers to a lot of different things. And so doing that in an elegant way, it takes a little bit of grace and elegance and it's more challenging in that respect."

Collider then asked if his approach to writing had changed at all. "I do an incredibly in depth treatment for every movie," Gunn revealed.

"I think of writing a screenplay as like creating the body of a human being, and you've got to start with the skeleton, the bones, and you've got to take a lot of time because that's the actual base of the movie. If you screw that part up, later down the line you're going to have a lot of mistakes."

Gunn announced the sequel and his return as writer and director back in April, when he revealed that "it will conclude the story of this iteration of the Guardians of the Galaxy, and help catapult both old and new Marvel characters into the next ten years and beyond."

The Guardians - Chris Pratt's Star-Lord, Zoe Saldana's Gamora, Dave Bautista's Drax, Bradley Cooper's Rocket and Vin Diesel's Groot - will next appear in 2018's Avengers: Infinity War opposite Iron Man, Thor, Captain America and many others.

They'll also appear in Avengers 4 a year later, before Vol 3 is released after that.