I gave the command seals over to Kirei. After my father died I gave up being a Master in the Fourth War. He said that 'A lot of things happened, none of them particularly glorious' and that your Master had you destroy the Grail.

. . . and then there was contaminated Grail mud, which is what caused the fire and tragedy. [ eyebrows knit together a little ] And that's also why Gilgamesh was still around, for those ten years between the wars.