Andy Pryor, the casting director, did not believe Michael Gambon would be available, and was surprised when Gambon accepted the role. Matt Smith, Karen Gillan, and Arthur Darvill were very honoured to work with him.
Steven Moffat said that this episode would be the most "Christmassy Christmas special ever," adding, "It's all your favourite Christmas movies at once, in an hour, with monsters and the Doctor and a honeymoon..."
Danny Horn admitted to actually being nervous about his on-screen kiss with Katherine Jenkins, largely because her boyfriend at the time was somewhat intimidating and happened to be on set that day.
Kazran's study was designed to be very large, as Kazran spent several scenes in there alone and would feel "dwarfed" by it. The walls were intended to look like copper that had turned green, which when combined with the red drapes created the Christmas colours of red and green.