Doctor Who will change forever after this season's dramatic finale, according to executive producer Steven Moffat.
Steven, who has also written episodes of the hit BBC show, has promised some big surprises at the end of this series, according to Digital Spy.
The writer, who is also behind cult series Sherlock, said the final episode, The Name Of The Doctor, would "change the course of Who forever".
He also said: "It's full of surprises and questions that have never been answered in the history of Who, including the Doctor's greatest secret.
"We'll also find out what makes his new companion [Clara, played by Jenna-Louise Coleman] so impossible and there's a surprise that no-one has got right so far.
"All I can say is that Clara hasn't just met the Doctor three times before."
Jenna-Louise's character has previously appeared on the sci-fi programme as space traveller Oswin and Victorian governess Clara, and the Doctor has spent recent episodes trying to find out why she has multiple identities.
The next episode The Whispermen features a brand new foe for the Doctor, played by Matt Smith, which Steven said will be terrifying: "Having brought back two of the classics, the Ice Warriors and the Cybermen, this year we wanted a brand new monster to create chills in the finale.
"And the thought of stylish, whispering, almost faceless creatures was an idea that firstly scared me and that I thought would work well in an episode that looks forward and back."