In case you weren't sure whether the two most fannish actors to ever be the Doctor got on well together, Moffat mentioned it to the Radio Times.
"David and Matt, I think... were both quite apprehensive of the other," Moffat told the audience at a Radio Times event earlier this month. "David's continued to watch Doctor Who like the sad old fan he is and so as far as he's concerned Matt's the Doctor. And of course for Matt, you don't believe yourself you're the Doctor, you just think David's the Doctor. So they were both slightly nervous and slightly apprehensive...By the end of it, Matt told me that he’d worked out this plan that they’d both continue in Doctor Who: do five individual episodes each and three together – would that be ok? It was a nice plan. I think if I’d said yes they’d have gone for it."
"The double act between them is sublime," said Moffat. "It’s one of those happy accidents – there’s no reason why they should be, but they are absolutely adorable and hilarious together."
Although we already sort of knew about the double act from earlier in the year...