Here's what I can tell you about this death:

* A current series regular is getting killed before the end of season five.
* The character who will die is someone who is much-loved by many of you fans.
* This is a real leaving-the-show death, à la Shannon or Charlie, not a quick-fix time-travel death like Jeremy Bentham/John Locke.
* The character getting killed off is not, I repeat, not Evie's character Kate Austen.

And a source close to the show tells me that the person who's being killed off just learned of their character's fate late last week, and the news hit hard. "Unfortunately, [he or she] found out after the sсript treatments were sent out to some of the crew on the set," says my source. "So it wasn't the best timing."