In the mid-series finale, it was revealed that River Song (Alex Kingston) is the daughter of Amy Pond (Karen Gillan).
Speaking to TV Guide, Steven Moffat said: “I used the name Pond for that reason, to create a link. [That reveal] was Plan A for a long time.”
He continued to say: “My favourite dirty joke in Doctor Who is the title of episode 13 in series 5, ‘The Big Bang’, [because it’s] the night when River began. I laughed a lot when I thought of that.”
He then went on to say that the link between River and Amy makes sense when looking back on past episodes: “I think that the moment that you actually see them together [you notice] how similar they are in certain aspects,” he suggested. “That sort of devil-may-care attitude, how naughty they are. Either of them, without the presence of The Doctor, would just be wicked.”