So, you guys know this scene. It’s pretty definite that we’re seeing Clara watching Ten in the Library, right?
But the thing is, he’s alone. And he’s not anywhere we saw in the episodes. And for the entirety of that story, he was either with Donna, or he was too busy running around rescuing people. Maybe he took a moment to stare soulfully out into the horizon between saving River and returning to the TARDIS, but I doubt it.
But what I think is much more likely is that we’re actually seeing Ten during his Farewell Tour in EoT. He’s dying, and going to say goodbye to all of his companions. But he doesn’t know how to find the younger River, so he goes to see her at the Library.