The Harry Potter stars made a dramatic entrance on a giant, purple bus for the launch of the Prisoner of Azkaban DVD.
In the freezing rain, Dan, Rupert and Emma arrived for the magical bash in London on the Knight Bus, which has a key role in the third Potter movie.
James and Oliver Phelps, who play the Weasley twins said: "The DVD is brilliant, especially the 360 degrees tour of Honeydukes sweet shop.
"The DVDs just get better. The deleted scenes are pretty funny too."
Other stars at the event included Matthew Lewis, who plays Neville Longbottom, Devon Murray, who plays Seamus Finnegan and Draco Malfoy actor, Tom Felton.
They were joined by the likes of David Thewlis, who plays Professor Lupin, Warwick Davis, who plays Professor Flitwick, and the rest of the Weasley clan.
The organisers of the event put on a great show for the world's media.
The set piece was performed outside, starting with smoke rising from the pavements to the sound of the Potter soundtrack. Then the Knight Bus hurtled around in front of the London venue, with Daniel Radcliffe, Rupert Grint and Emma Watson waving frantically from the platform as cameras snapped away.
Some of the stars then chatted to Newsround about what they were up to and what it's like filming the FOURTH Potter film, the Goblet of Fire.
Honeydukes sweetshop was re-created at the party!
Rupert told us: "We're about halfway through filming now, it's going really well. In this one you've got the Yule Ball, where we all have to find partners so that will be quite interesting. And I have to wear these horrible dress robes for the ball so I'm not really looking forward to that."
Emma told Newsround that she was learning new skills for Hermione for the next movie - learning to dance! "And it's not just normal dancing, I'm talking the tango, the foxtrot, waltzing, it's quite impressive," she laughed.
In fact, all of the cast agreed they were having loads of fun on set at Leavesden for film four, and that new director Mike Newell was "crazy and fun".
For now though, Potter fans will just have to enjoy the third DVD.