Lost: Which 2 characters are siblings?

This is a major spoiler for Lost, so do not read on if you don't want to know.

Ok, you have been warned. :-)

Two major Losties are siblings, and we are gonna find out (via flashback) before they do.

No, it isn't long lost brothers Sawyer and Jack (but what an interesting story that'd be) it is Claire and Jack that are brother and sister. Yes, this has been hinted at before in Season 2 but in an upcoming Claire episode we will find out all about it.

So baby Aaron has an Uncle Jack now, Oooh Cute! I hope 'Uncle' Charlie isn't too jealous.