I thnk he didn't know, yet. When I watched the clip, Bush got the note, took off his headphones (and he had a rather dour look at the time while HE was listening), turned to Rumsfeld, grinned, and then turned to Blair and whispered to him, shook his hand, and grinned. Powell was still listening and hadn't been told yet.
Oh dear DU is going to be upset.