Rupert spoke to CBBC Newsround's Lizo Mzimba about what he gets up to when he's not busy being a film star and how he really hated filming scenes with spiders in.
How does this film compare to doing the first one?
It was a lot more fun because we were a lot more comfortable with working, I guess - because of working with Kenneth Branagh, who's really funny, and more confident with the camera.
What was your favourite scene?
Slug scene, definitely. That was so fun because they had all these different flavours of slug slime. There was chocolate, there was lemon, there was orange, there was peppermint. All these different flavours - they made them taste really nice.
You're scared of spiders - what was it like doing scenes with them?
I hate them - even rubber ones I get scared of. Luckily some of them were CGI [computer graphics]. But that big car-sized one, that was actually there unfortunately. So that wasn't my favourite scene to film.
Did it help your phobia?
What's it like now being back at school, now you're not filming?
It was weird to start off with. My friends have been great - they treat me normally. The teachers suck up, they really do. But other than it's been fine.
Did they deliberately give you all the funniest lines?
I think that's just his character I think, which is good.