Michael Fassbender (Magneto) and James McAvoy (Professor X) have also answered fans' questions on the official Facebook page. You can read their responses below:
Kristine: How did you find your "dark side" in playing this role?
There's a dark side in everybody. You just have to dig deep and get involved in it. Any time you get a role, you realize three main characteristics of that person, and then you just have to inflate them in yourself if they're not there or just use them if they are already there.
Maddie: Does the fact that the character you play has a very established future already as a super villain help or hinder the way you portrayed him?
Neither, really. I got all my source material from the comic books.
Dominic: What was the hardest part of playing Magneto?
Trying to bend metal when obviously I can't do that.
Chris: After playing Magneto, do you feel some type of connection with the character?
I absolutely feel a connection. I think the interesting thing about Magneto is he does magnify the human race's failure in trying to co-exist and then magnifies the destructiveness. Even though his methods are extreme, his arguments actually are true and make sense.
Kenoll: What did you feel when you put on the helmet for the first time?
You feel a little bit silly, but then you just have to sort of throw yourself in there and really have fun and own it.
Anonymous: Does your character wear the helmet a lot in this movie?
No. This is the transitional period. He is still learning how to use his power just like everyone else. By the end of the movie he is definitely using it though.
Andrea: What do you believe was the most entertaining part in playing Magneto?
What's very encouraging as an actor trying to approach this part, is that there's so much material there in the comic books that you can very easily form a character and know exactly where he's coming from. In that respect you can just get on with it and enjoy being the person.
Marcus: Are we going to see Erik/Magneto as a possible team leader like Cyclops or more of an outcast trying to fit in?
I think all of the mutants are outcasts trying to fit in, but within his own peers, I think he's a definite leader. There's no doubt about that. I think any megalomaniac that manages to get an army behind him the way he does has to be a good leader. I think he's charismatic, I think he's intelligent and I think he's very forceful. That's a pretty influential combination.
Rebecca: Will Erik have a love interest?
Not really. I think there are signs of seeds to be sown later, but I think when we meet Erik in this film, his life is more about revenge than anything else. In this film, he's a lone wolf and he's on a very specific mission and he's Machiavellian in his approach to whatever ends justify the means.
Aaron: Charles Xavier/Professor X and Magneto were once like brothers. Do we get to see what made their friendship falls apart and what made that happen?
Yes, we get to see why they want to be friends. You see the moment they meet. You don't just start the film and they're buddies. Which I liked. But we do also get to see what makes it all fall apart. We get to see something quite tragic because it's not a small thing that makes it fall apart, but it's only one element in their relationship. Everything else in their relationship is pretty solid and pretty positive. So it's quite tragic that they can't put their differences aside about how to move forward as a new species. Their approaches are so fundamentally different that they can't reconcile them and it has tragic consequences.
Anonymous: What was it that initially attracted you to the role of Charles?
The opportunity to take a character who we are very familiar with and turn all that on its head. The Charles we know as an older man is portrayed in a way that is very straight, very noble, very wise, very sage; and I had the opportunity to make him very unwise and very unknowing and very glib, rather than sage. And not meaning make him stupid – he is a genius – but I think at this stage in his life he is more selfish. And also it was great to have fun with it, of course. To make the character a little more fun than we are used to seeing.
Anonymous: What was the most exciting and fun part about playing a young Charles Xavier?
Playing somebody who thinks he's always right, and then gets proved wrong quite a lot is really fun. Also knowing that you are taking over from Patrick Stewart, and that you are being trusted to re-invent this character that people have such a solid idea of is really quite exciting. It's not that I'm going to try to a create a new thing for them, but it is more about being trusted to satisfy the fans that exist and that have been there since the comic book and cartoon days. That's quite a big responsibility that is quite scary. Anything that has fear attached to it is usually quite fun. And at the same time it's exciting that I will be introducing a lot of younger audiences – who didn't necessarily see the other films – to this iconic character.
Ashton: What was it like trying to simulate Charles Xavier's power of telepathy as an actor?
Charles is one of the most powerful mutants in the world, if not the most powerful. So I tried to make it look like it was really easy and more like it was just an extension of Charles himself. But when he's really struggling with the power, the execution of his mental ability becomes a little bit more physical due to the strain he is enduring in harnessing the strength of his power. At those points it ends up being expressed physically.
Harris: Are you taking a different approach to the character of Charles Xavier from the way fans are used to seeing him portrayed? How much did you want to capture the feeling of Patrick Stewart in performing Professor X?
I didn't want to capture too much from Patrick Stewart's characterization. I wanted to mold it as much as possible. The main thing that I had to respect in Patrick's performance was the fact that he played Professor X as English and we had to keep him English even though the Professor in the comics and cartoons is actually American. Other than that, I didn't want to take anything else from what he did with the role really. I did want to go bald, but I wasn't allowed! Hopefully that will happen in the next film. The real joy of doing a film like this is to show how different the characters are in the beginning compared to where they end up. By the end of this film we are really connecting all the other X-Men films together, and by then I am playing Professor X much more like Patrick Stewart's Professor X. Because he evolves into that man by the end.
Morgan: If mutations and the X-gene really existed, what do you think your ability would be?
I would like to inspire love. I would quite like to be able to make people fall in love, sort of like Cupid. I guess it's not a superhero or mutant that exists, but maybe my mutant name would be Amore.
Nick: Can we expect to see you do some sort of mental battle with Emma Frost?
Yes, you can. But that's all I'll say!
Kris: What was it like winning the role of young Professor X?
Exciting. But it also filled me with a great sense of trepidation because I knew I was toying with the loyalty and affections of all the people who have made an incredibly big and successful franchise, filled with all these really established and adored characters. So there was this huge weight of responsibility. But it's quite good fun because it gets you a little bit scared and you find yourself thinking how fantastic and exciting the opportunity is, but at the same time you really want to make sure you don't screw it up!
Victor: In this film will we see Charles Xavier also as a teacher or is he just a mutant discovering and controlling his power?
He's a mixture of both. Xavier is probably the least mutant-like mutant of the lot of them. But the thing about X-Men is that everybody's a misfit. They've always been outsiders, they've always been on the run, they've always been bullied and scared of what they are; and scared they can't control whatever power they have. But Professor X never really feels that way. Professor X has always been the guy who is proud of being a mutant, and he knows he is probably the most powerful of them all. Charles is much more comfortable with it and embraces that Professor role. So while we do see him developing his powers and learning to harness them, he's pretty much come to terms with his powers when we meet him. But we also see him as a teacher because he finds that it is his passion. He wants to not only be at the forefront of this emerging part of society, but he also wants to help shape it.