Me and my friend were discussing who the wee girl, who regenerated at the end of "Doctor Who: Day Of The Moon", which aired 3 weeks ago on BBC1. I say that she's got something to do with River Song, but then I said she may be The Doctor's secret love child.
My friend made an interesting comment, he said that she might even be The Master's daughter. Now that would be amazing if she was. It would also be very interesting to see how that would pan out in the new series, as it goes on.