Koschei could barely compute that. Barely. But the intensity with which it impacted him when he finally did compute it was enough to knock him into the sitting position. His arms loosened briefly before his gaze turned to the Doctor before shifting a bit closer and raising one of his hands to slowly run through his hair.
There was nothing that he could say that would help in this situation.
Nothing.
So he just hugged the Doctor and let him breakdown.