Four flush cards on the board....

Last night I was on Pacific Poker on an NL$50 table, when I hit AA. I raised the pot and a short-stack called me all-in. I was re-raised by a third player, who I then raised all-in. Both players I was in the pot with had pocket 99's, making them both dead to 4 cards for a striaght, or 4 flush cards. The third player ended up hitting 4 cards for a flush and taking the pot. I was just wondering what the odds are of four (or more) of one particular suit hitting like this?