A new Doctor Who video preview for this Saturday's series finale has been released - with Matt Smith and Jenna-Louise Coleman hinting at what to expect from Steven Moffat's The Name of the Doctor episode.

"The finale is epic - it is such a treat for all of the fans," says Coleman, who plays the Doctor's companion Clara.

"I think throughout this season, we're building up to the revelation in the last episode - and then it kicks us on somewhere else," added Smith.

Moffat has promised that The Name of the Doctor will "change the course of Who forever".

"It's full of surprises and questions that have never been answered in the history of Who, including the Doctor's greatest secret," claimed the sci-fi show's showrunner.

Doctor Who's The Name of the Doctor airs this Saturday May 18 at 7pm on BBC One.