[She just casually files away the fact he's just referred to Brax as his brother, and smiles right through it. She hadn't actually known that fact, so she's surprised to hear it, but she supposes things make more sense knowing they have that bit of relation to them.]

You won't lose her. Not now. But eventually -

[She cuts herself off there, reminded of some of the thoughts she had been hit with during her talk with Charley. She frowns, giving a shake of her head.]

Eventually you'll regenerate and meet Rose, meet Professor Song. You'll even meet three versions of my face, not that it's the same as you and Charley. It's just...you'll let her go eventually.

[Unless he never leaves Asgard. She's starting to like the sound of that, for him. For all the Doctors, really.]

But while you're here, Doctor, I promise that you won't lose her. I won't allow it to happen.