Rupert Grint plays Ron Weasley in Harry Potter and the Goblet of Fire.
Newsround chatted with him to find out about his big row with Harry...
You can also watch our interview with Rupert in full by clicking on the Newsround Player link on the right and selecting Potter.
This a very different kind of film. For a start Ron and Harry fall out big time. What was that like to do?
That was good fun actually. I suppose the whole film is more grown-up and all the kids are teenagers now. We clash quite early on in the film, I think Ron gets a jealous because of the whole Tri-Wizard tournament.
That was something we hadn't done before in the other films, so that was quite good.
It must have been quite different to do because you and Dan are very good friends in real life, and Harry and Ron are normally so supportive of each other. Did it kind of break it up, being able to do something like that?
Yeah, it was quite good actually, it was a bit of a change, which was quite good.
The other big thing in this film is all the romance going on. Do we see any hints about Ron and Hermione and are you trying to hurry this process along?
That was quite a major part for Ron, because the whole Yule Ball thing, because him and Dan (Harry) have to get partners for the dance and they find it quite hard. And Ron's really jealous of Hermione as well, so there's still that sort of thing happening.
How long did it take you to learn and practice all that ballroom dancing?
They had a choreographer come on and he was teaching everyone to dance, but I got out of it because Ron doesn't dance in the Yule Ball because he has to be peed off and miserable throught the whole thing.
Are you disappointed you don't get to dance?
I do get one chance to dance, I had to dance with Maggie Smith. That was the only dancing experience I had, which was actually quite enough really.
This film is on a much bigger scale, was it much more intense to do, with a bigger story and with so many big sets?
Yeah, there were a lot of action scenes. All the Tri-Wizard scenes they were pretty intense, and the World Cup scenes as well, like on the campfire scenes.
When the Death Eaters come on they were blowing up tents and setting fire to things. That was quite a exciting scene to do.
How long do those things take, because they go past so quickly in the film?
Well the whole film was quite long to make. The whole thing took close to a year to make. I suppose the big scenes, some of them could take about two weeks to do.
You've got the fifth one coming up, is there anything you're looking forward to?
Yeah, the fifth one. I'm looking forward to doing the Quidditch, that should be quite good, because I think it's Ron's turn to have a go at that.
And lots of choruses of Weasley is our King?
Yeah, exactly.
Do you think it's a possibility that you might do all seven?
I think I want to do them. I want to do as many as I can because they really good fun to do and obviously we've got to know each other really well, the whole cast and some of the crew, we're really close.
With the whole Ron and Hermione thing, we've seen in the books how that's going, how do you personally feel about that. Is that something you're looking forward to, or is that something you with JK hadn't done?
It's quite fun at the moment, at the moment it's just sort of subtle. But I don't what'll happen in the future, who knows?
And how does Emma feel about this?
I don't know ... she's probably looking forward to it very much!
How do reconcile your life in the films with the things you do as a normal teenager, how difficult is it to have a normal life?
It's a little bit different now. The only thing really is getting recognised when you go out, that's quite hard to get used to. But they're usually nice about the film, so it's never been that much of a problem.
What's been the highlight of this particular film for you, what did you enjoy the most?
They gave us all diving lessons and that was really good, because I've never done anything like that before and that was a whole new experience, that was quite good.