Joe Russo says the "hardest part of the job" of making 'Avengers: Infinity War' was combining all the different Marvel Cinematic Universe narratives.

The next two Avengers movies have been announced as the end of Phase 4 in the MCU and the filmmaker - who is helming the two films with his brother Anthony Russo - said everything has been leading up to 'Infinity War', but it's a complicated journey.

Speaking to Comicbook.com, Joe said: "Everything is setting up 'Infinity War'. Every narrative that you have seen in any of the Marvel movies leading up to this point comes to bear in some way because all of the characters and all of the franchises are coming together, bringing their themes and their tone and the things that motivate the characters are driving them through this story. It has been the hardest part of the job for us, is melding all of that together. But thankfully we got Christopher Markus and Stephen McFeely working with us.

"They are incredible collaborators. They wrote 'Captain America: Winter Soldier' for us and 'Civil War'. Now they're writing both 'Avengers' movies. I feel like we've got a great Vulcan mind meld between the two of them, and me and my brother."

'Avengers: Infinity War' will see the hero squad - Iron Man (Robert Downey Jr.), Captain America (Chris Evans), Thor (Chris Hemsworth), The Hulk (Mark Ruffalo), Scarlet Witch (Elizabeth Olsen), Vision (Paul Bettany), Black Widow (Scarlett Johansson) and Hawkeye (Jeremy Renner) - join forces with the Guardians of the Galaxy.

The two teams will have to work together to fight Thanos, with some help from newcomers Spider-Man (Tom Holland), Black Panther (Chadwick Boseman) and the screen debut of Captain Marvel (Brie Larson).

Russo also revealed at San Diego Comic-Con that 'Infinity War' is currently the longest 'Avengers' movie so far.