AA vs 5 opponents 20/40

[Dugalufagus]

I have a solid image in 20/40 game at Hawaiian Gardens. I pick up AA UTG, raise and get called by 5 players including the big blind who appears to be a pretty straightforward tight player. Flop is K,5,6 rainbow. BB checks, I bet 3 players call and BB check raises, I 3 bet. All but 1 player call including BB who comments "everyone got King." Turn is K and he bets. What do you do? My thinking with the comment is that he has either a K or he flopped a set. Could he possibly have 7,8 and make a brilliant bet against what appears to be either AA or AK hoping to fold AA and play against the other players who are very unlikely to have a K?