Trip aces flush hits on river, this sucks.

[Mossberg]

I prefer to bet small on this river. worse aces and kings will pay you off, and if he raises you can be pretty certain you're beat. As played, you've let him represent the flush. It's a really [censored] spot, but given that he could have already been slowplaying a monster, and his hand DOES look like a completed FD, I think you can just fold to his overbet.