[Glenn.]

Matt Smith has described Doctor Who's upcoming sixth series as "harrowing" for the Time Lord and his companions.

Bang Showbiz quotes the 28-year-old actor as saying that the Tardis crew will be facing several very dangerous adventures when the sci-fi drama returns this spring.

"The Doctor and Amy (Karen Gillan) are going to be faced with some really harrowing and seismic choices about their relationship and who they are, and why they are important together," he said.

Smith also promised fans that the new series is to feature a terrifying new enemy who he predicts will rank among The Doctor's most menacing foes.

"I do think we've got one of the greatest monsters, especially during my tenure on the show, but I think in the history of it. It's a real cracker," the star remarked.

Earlier this week, Smith vowed that fans will be satisfied when Professor River Song's (Alex Kingston) true identity is revealed.

Doctor Who returns to BBC One in the UK and BBC America in the US in the spring.