flopped "nuts" facing a big raise

[forssell]

10-20 online. Utg+2 opens to 60, I call MP with 99, Villain calls in CO , bb calls. Pot 247. Hero and villain have ~3200 left. Flop comes Ac9c2d. Checked to me, I bet 225, CO raises to 1200, others fold. I had been playin for a while but hadnt seen anything out of the ordinary by villain, gotta admit that I hadnt been paying attention as good as I should have. The overbet got me really confused and I had a hard time coming up with a good line. Suggestions?