He doesn't remember their last adventure and only gets her note that she's leaving him.
Wait. But you... [Her eyes go wide and and she jumps up, notebook and pen scattering to the ground.] You're talking as if you do know me. As if you know what happened. But that's impossible. You died. I saw the TARDIS get...eaten. I kept hoping, but then I met another you, a younger you. Which...you wouldn't remember.