Matt Smith has said that River Song should never become a full-time Doctor Who companion.
Song, played by Alex Kingston, only appears when the Doctor needs her most, something that Smith feels adds to the character's appeal.
He told Bang! Showbiz: "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.
"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."
Smith also expressed his desire to see the fiftieth anniversary show of Doctor Who shot in 3-D.
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