ok, very early speculation, but I thought I'd share it with you all 
ok, the 12th episode is called The TimeWar. in the daily mail today it said the Doctor will become a Dad, so this probably means we'll meet his family.ok, so putting all this together with the face of boes secret that is more than likely to be "you are not alone" i've come up with this conclusion...
the face of boe's secret is "You are not alone" meaning that a time lords still alive. Then in the time war the 10th doctor gets dragged into the time war again somehow and has to save himself or something Then at the end it turns out his that son/daughter/granddaughter ect. actually manages to survive, but the doc didnt know that before.
and more than likely this is because the doctor only has a few regenerations left, they need to continue the shoe show how, thus bringing in another timelord/lady i.e susan, his grandaughter. which could possibly be played by Billie Piper, since she wanted to be a female doctor if she ever came back

ok, the 12th episode is called The TimeWar. in the daily mail today it said the Doctor will become a Dad, so this probably means we'll meet his family.ok, so putting all this together with the face of boes secret that is more than likely to be "you are not alone" i've come up with this conclusion...
the face of boe's secret is "You are not alone" meaning that a time lords still alive. Then in the time war the 10th doctor gets dragged into the time war again somehow and has to save himself or something Then at the end it turns out his that son/daughter/granddaughter ect. actually manages to survive, but the doc didnt know that before.
and more than likely this is because the doctor only has a few regenerations left, they need to continue the shoe show how, thus bringing in another timelord/lady i.e susan, his grandaughter. which could possibly be played by Billie Piper, since she wanted to be a female doctor if she ever came back




well I assume she is, since shes a timelord too according to another forum