This community is dedicated to the (canon, I'll have you know) pairing of the Doctor and his "future companion" River Song. The character of River Song "ran" for two episodes, having met the Doctor before he had met her. This is the thing that begins the Doctor's "affair" with her. Sadly the Doctor meets River on the day that she dies, therefore having to live through their whole time together knowing how she dies. Yet she makes him promise not to alter the time line. The Doctor, the future Doctor, uses this time to find a way to save River Song so that she might live on after death, by giving her the sonic screwdriver, containing her data ghost.
The current Doctor's only clue to who River Song is to him in the future is that she holds the greatest secret of all: she knows the Doctor's real name.