KK - dreaded ace hits turn

Party 2/4

I hadn't been at the table too long but reads so far:

UTG+1 seemed solid with big stack
SB was a loose passive fish
BB was a loose passive fish

Hero is MP2 with K [img]/images/graemlins/club.gif[/img] K [img]/images/graemlins/heart.gif[/img]

Preflop: UTG folds, UTG+1 raises, 1 fold, Hero 3-bets, 4 folds, SB calls, BB calls, UTG+1 calls.

Flop: 7 [img]/images/graemlins/diamond.gif[/img] 7 [img]/images/graemlins/heart.gif[/img] 3 [img]/images/graemlins/spade.gif[/img]

SB bets, BB raises, UTG+1 3-bets, Hero calls, SB calls, BB calls.

Turn: A [img]/images/graemlins/club.gif[/img]

SB checks, BB checks, UTG+1 bets, Hero???

Now I'm wondering what UTG+1 was 3-betting with on the flop and whether I have him beat or not?

Also should I be capping this flop?