In The Big Bang, after the Universe has been rebooted, the Doctor says:
Space and time isn't safe yet. The Tardis exploded for a reason. Something drew the Tardis to this particular date and blew it up. Why? And why now? The Silence, whatever it is, it's still out there and I have to --
(He's cut off by his phone ringing.)
In the next year we do find out what the Silence is (are?), but the entire plot of the Tardis blowing up is dropped.
Have we found out why the Tardis blew up, or was that just glossed over or left out?