Flopping a Straight Flush....

I was playing earlier and the following hand occured...

PokerStars Game #8899057663:
Tournament #45257507, $20+$1 Hold'em No Limit - Match Round I, Level I (10/20) - 2007/03/14 - 13:35:03
(ET)Table '45257507 1' 2-max Seat #2 is the button
Seat 1: englishgc (1600 in chips)
Seat 2: United113 (1400 in chips)
United113: posts small blind 10
englishgc: posts big blind 20
*** HOLE CARDS ***Dealt to United113 [8c Tc]
United113: calls 10englishgc: checks *** FLOP *** [9d Td 7d]
englishgc: checks
United113: bets 60englishgc: calls 60
*** TURN *** [9d Td 7d] [3s]englishgc: checks
United113: bets 100englishgc: calls 100
*** RIVER *** [9d Td 7d 3s] [2s]
englishgc: bets 180
United113: calls 180
*** SHOW DOWN ***englishgc: shows [8d Jd] (a straight flush, Seven to Jack)

Now apart from the bad call by me on the river (this guy had been putting loads of river bluffs all game though and i had top pair!!) I have never seen it before when someone had hit a straight flush on the flop..

He was holding Jack Eight of diamonds

Flop 9 10 7 diamonds...

Now i am NOT great at working out probabilities.. but he could only hit 9 10 7 diamonds or 9 10 queen of diamonds to make this... 48 cards in the deck and to hit the exact THREE cards you need????

Does anyone have a clue of the odds of this?? Has anyone seen this before???