Matt Smith has been talking to Entertainment Weekly.com and has been revealing some bits of info about the upcoming series. Here's what he had to say about The Doctor's Wife:
One of the episodes in the new season was written by comics legend Neil Gaiman. What can you tell us about that?
Well, um, not a great deal, as always. Sorry to be a pain! But we were thrilled to get a writer of his sci-fi stature and magnitude on board. And he’s applied his rather brilliant and mad brain to a brilliant and mad idea. All I can say is that the Doctor spends a lot of time with the Tardis.
Michael Sheen is in that episode. What was it like acting with him?
I didn’t, actually. Because he came in and did a voice for it. So I didn’t get any actual scenes with him. Which is a shame. But, god, it’s a real coup to get an actor of his quality.
You can also read a fascinating interview with Neil Gaiman on the same episode HERE. Now, normally I wouldn't speculate but the line: "All I can say is that the Doctor spends a lot of time with the Tardis," does make me wonder if Idris (Suranne Jones), the "old acquaintance with a new face", is in fact his TARDIS... Speculation over.