Back in February we posted this Big Rumour. We've now confirmed with multiple sources that this appears to be true. The only part that is still speculation is the list of survivors which was just guessed at by the original poster J, but everything else appears true.
It's funny looking back at the comments in the Rumours page the number of people who cried fake.
As this involves potential death spoilers we've put this behind the usual Are You Sure button.
He told me the following:
1) That he was playing one of Widmore's goons.
2) He and a few other fellows were having a shoot-out on the island with some of the Losties and that his character is responsible for wounding Kate (he called her Evie) in the arm.
3) That the Losties will board the sub (obviously a new one, since the last one was blown-up).
4) That Flocke gives Jack a backpack that Jack takes on the sub with him.
5) Unknown to Jack, the backpack has a bomb in it.
6) The bomb explodes and only 5 of the Losties survive. He said he thinks the five who survive are Jack, Sayid, Hurley, Kate and Claire but is not sure. (I cannot imagine how he would know this...seems like he left out some info.).