Steven Moffat always intended River Song to be a recurring character during his turn as show runner, and he had planned that she would be the Doctors future companion's child for a long time prior to its ultimate reveal. Amy was only given the surname Pond to create a link between the two characters. Alex Kingston always knew more of River than any other actor. Filming the sixth series, Kingston knew of Rivers relationship with Amy and Rory, whilst Karen Gillan and Arthur Darvill only found out upon reading the script for the mid-series finale. Interestingly, many theories swirled about the internet pertaining to Rivers identity. Many thought she was the Doctors wife, whilst many others believed her to be his killer. A few, though not many, did guess that she was Amy and Rorys daughter. Ultimately she became all three.
