Last week, fans were treated to a slew of new photos and details for Captain America: Civil War, just days after the first trailer was released. Over the weekend, director Anthony Russo made an appearance at the Comic Con Experience in Sao Paulo, Brazil, where he revealed new details about his highly-anticipated Phase Three adventure, hitting theaters on May 6, 2016. The director says that his sequel is one of the most "serious" ever produced by Marvel, but there are plenty of humorous moments, provided by Ant-Man (Paul Rudd) and Spider-Man (Tom Holland).

"The film definitely has a more serious tone I think than any other Marvel [Studios] movie yet. And that's kind of natural to the process because you're really gonna turn these heroes, who have been friends and partners, against one another. And if we're gonna have them fight for a whole movie to the end, there has to be a serious issue because these are smart people, they're likeable people; they're not villains, they're good guys. And so you have to think very hard about a very complex situation that's gonna put them in conflict with one another for an entire movie. At the same time, not all the characters in the movie have the same investment in the conflict. There are certain characters that come into the story a little later who don't have the same baggage that the Avengers have in terms of what's going on in the film. So they don't have as much darkness to deal with in the film, so they can be a little lighter and more fun. I think the movie has a healthy balance between very serious, interesting and very surprising storytelling, and sort of light, fun wits and humor. Characters like Spider-Man and Ant-Man enter the story a little later."
RELATED: Is Civil War Technically an Avengers Movie? MCU Fans Fiercely Debate the Question

After years of waiting, Marvel announced in February that Spider-Man will be part of the Marvel Cinematic Universe, debuting in an MCU movie later confirmed to be Captain America: Civil War, before starring in a new Spider-Man reboot, produced by both Marvel and Sony Pictures. The deal was made just months before production started in May on Captain America: Civil War, but Anthony Russo revealed that the web slinger was always a part of the story they wanted to tell. Here's what the director had to say at the Comic Con Experience this weekend.

"From the second we had the idea to do the story of Civil War, Spider-Man was a part of the story. It was a very complicated business arrangement for Marvel Studios to be able to use Spider-Man from Sony. So, we were always told by Marvel 'Don't count on it, you may not get to use Spider-Man, so you better have a plan B' And we were like 'Okay, we get it, we have a plan B if we don't get Spider-Man; we'll figure the movie out.' But the truth is, we never had a plan B. We only have envisioned the movie with Spider-Man. He was always a part of the story. It was very important to us to reintroduce the character. We cast him young, Tom Holland is a young actor; a teen himself, and we really liked playing into that nature of the character and we think it makes him very special in the universe of the Marvel characters. I think people are really gonna love Spider-Man in this film."

Aside from Spidey, another character making his debut in Captain America: Civil War is T'challa (Chadwick Boseman), who will go on to star in his own Black Panther movie, slated for release on February 16, 2018. We know that Black Panther is technically on Iron Man's side, along with War Machine (Don Cheadle), Black Widow (Scarlett Johansson) and Vision (Paul Bettany). They will be going up against Team Cap, which includes Hawkeye (Jeremy Renner), The Winter Soldier (Sebastian Stan), The Falcon (Anthony Mackie), Sharon Carter/Agent 13 (Emily VanCamp) and Ant-Man (Paul Rudd), but we reported last week that T'challa never quite makes up his mind about who to fight with. Anthony Russo revealed that Black Panther has a very important role, and that he is introduced very early.

"We couldn't be more excited to bring him to the screen for the first time. He's very central to the story. He comes into the story pretty early, but what's great about Black Panther in this film is all the other characters break down into two sides - Captain America's side and Iron Man's side. Black Panther never quite chooses a side, he's sort of on his own side for the whole movie which makes him very cool in this storytelling."

Captain America: Civil War will have one of the largest ensemble casts in MCU history, with almost all of the Avengers, past and present, except for Hulk and Thor, along with Spider-Man, Black Panther, Ant-Man, General Thaddeus Ross (William Hurt) and a mysterious character played by Martin Freeman. Anthony Russo revealed that the massive cast posed a number of problems finding ways to showcase all of these beloved characters, some of whom will be more prominent than others. Here's what Anthony Russo had to say about creating a balance with the cast.

"It's really difficult. They're all amazing characters, we and the fans love all these characters. They're played by amazing actors, so as filmmakers and storytellers, we have to give all those characters their due. You have to come to this movie; you've got your favorite characters. You want to see them do something amazing, have fun with them, be surprised by them. Our job as storytellers to figure out how to give you that experience. Some people have more prominent roles than others in the movie; Captain America has the most prominent role. Iron Man is the next most prominent role because he has that primary point of view that's pushing against Captain America in the film. And then the other characters kind of fill in around them, but I think all of them have great moments. So, whoever you love, hopefully you'll leave the movie happy."

The director also teased that Scarlet Witch (Elizabeth Olsen) and Vision (Paul Bettany) have "strong stories" that will "cross" at some point in the movie. In the comics, both Scarlet Witch and Vision became romantically involved, so it's possible this story will be showcased in Captain America: Civil War. What do you think about all of these new details?