"No, no, not a child. He's all grown up, and sane, and still calls himself Koschei, which is an absloute delight! It's like everything that went wrong in the Master didn't go wrong in him. Well, as much as I can tell, as I didn't spend all a huge amount of time with him. Just an hour or two. Talking, mostly."
The Doctor rotated, her shoulder and head still leaned against the glass, watching Kurt. "He even has a TARDIS with the chameleon circuit still working. I don't know that mine has worked in...well, in centuries, at least."
She paused, a curious expression on her face. "An eight-year-old Koschei is here? Does she already here the drums? Oh, I hope not, that was so hard, they took her away from me, changed my friend so much. Not my friend anymore, and I miss that sometimes. She could have been so much, and she's just..." The Doctor shrugged. "Lost."