'Doctor Who' Matt Smith: 'River Song shouldn't be full-time companion'

Doctor Who star Matt Smith has expressed his belief that River Song (Alex Kingston) should never be one of The Doctor's full-time companions.

Smith explained that part of River Song's allure is that she suddenly appears when The Doctor needs her most.

"I think River's too independent to ever be a full-time companion; I think that's what makes River great as a character. The companions and The Doctor are doing their thing, then whoosh - in comes the hair," Bang Showbiz quotes Smith as saying.

"It just messes The Doctor up and makes him go, 'Oh Christ, River's here', and it frightens him. And weirdly he's going, 'Why the hell am I attracted to her? What's that?' That's the woman who makes him go whoa."

River Song first appeared in Doctor Who in the Tenth Doctor two-parter 'Silence in the Library'/'Forest of the Dead' and has since returned for several adventures with Smith's incarnation of the Time Lord.

Last week, Smith claimed that The Doctor can often be a "destructive" force to those around him.

Doctor Who continues on Saturday with the episode 'Night Terrors' on BBC One in the UK and BBC America in the US.

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Watch Doctor Who's Karen Gillan discuss the show's return with Digital Spy below: