"Absolutely," he agreed, with a rueful little smile. "Just like I need to remind myself that all the versions of the Master I've seen around here are just possibilities. My universe may just be the one where I manage to find him and sort him out so we can be friends again without destroying half the universe in the process. You never know."
He grinned, rather shamefacedly. He was only sort of joking. He had to let the Master go. He realised that now.