David Tennant felt like spiritual medium Derek Acorah in 'Fireman Sam: Alien Alert - The Movie'.
The 'Harry Potter' actor portrays alien hunter Buck Douglas in the movie and he loved playing the extraterrestrial seeker and TV presenter - who is similar to Derek, former host of 'Most Haunted' - and bringing a "sci-fi slant" to the popular children's TV series' film spin-off.
He said: "I guess you could say I play the Derek Acorah of the alien hunting world in the new movie, which is a lot of fun!
"Fireman Sam is a true institution of children's television and a series that's much-loved by all in our household. The new movie takes us to new levels of excitement with a sci-fi slant that includes new characters, rescue vehicles, locations, and plot twists."
The 46-year-old actor - who is known for starring in 'Doctor Who' as the Tenth Doctor, a time-travelling alien - finds it "tantalising" that there could be an extraterrestrial life form in existence, and loved bringing the subject matter to the movie.
He added: "We are fascinated by the idea of aliens, aren't we, the idea that there is something out there that we don't understand and also that there might be another world like ours but different. It's tantalising. It's a little bit scary too, but I think the sense that we don't want to be alone, you know, we want to feel like there is untold mysteries out there to discover somewhere."
The film sees the Pontypandy residents get a little over-excited at the prospect of featuring on Buck's 'Alien Quest' TV show when he arrives in the town.
Fireman Sam - voiced by Steven Kynman - sets off to find out what's behind all this sudden alien activity, but when a big stunt goes wrong and causes a forest fire, the team have to work together to get everyone to safety.
'Fireman Sam: Alien Alert - The Movie' is out on now on DVD.