Unbelievable

Ok heres what happend.Blinds was 150/300, with 4 players still in. I come across POCKET ACES, so i raise 1500, and the second player next to me raised it to 2500, the third player folded, and the fourth player re-raised all-in. we all practically had the same amount of chips on table so i move all-in, the second player called.
This was all PRE-FLOP. So now we get to see eachothers cards now. The second player had Pocket KINGs, and the other player had ACE heart DUECE spade. Flop comes out KING heart.Queen spade.NINE heart.
Turn comes FIVE heart.
River......THREE heart
So The Fourth player wins by rivering ACE high flush.
I dont mind losing to a set of KINGS. But i think its UNBELIVABLE that someone had the guts to go ALL-IN with ACE DUECE Pre-Flop.