Sebastian watched as Ciel played against the ghost. It was times like these, when Ciel used him as an object, that Sebastian almost, almost regretted his contract with the young lord. In many ways, the two of them were fit for each other. Sebastian's demon nature made him a bit blood thirsty and he got a sadistic pleasure out of the things his bocchan asked him to do. Ciel Phantomhive had been hurt and used and had lost any sense of childlike innocence that he may have had before. There lied a bit of a sadomasochistic relationship between the two that worked in its own odd way.
The good king made his final, and winning move, and Bocchan looked quite surprised. He even stammered out an insult to the King of England. Sebastian was quick to step in and save him once again.
Ciel traded Sebastian. Sebastian would make sure he paid and thought twice about using him unfeelingly. Just a small reminder of who he was and what he was owed.