Grand Master is also mentioned a few times in the game or at least he is when you import your TW1 game (can't quite remember with a stock TW2 game). ›››
Yeah, like when Geralt wonders why Radovid took the Order in when he had seen the Grandmaster's madness. Also some books metioning the Viziman Uprising.
But I like that quote about Cedric, it's quite subtle. Geralt, having seen how an innocent boy became a madman, knows the danger of uncontrollable visions.