Once upon a time, mystery fans had to solve puzzles on their own; now, you not only didn’t need to be the one to solve it, you didn’t even need to be hanging around on the website where someone else had solved it. An Ana Lucia flashback episode in the second season showed Jack’s father, Christian, visiting a blonde Australian woman. Not long after it aired, I saw someone on the Television Without Pity message boards passing along a theory they had read on a different site suggesting that this woman was Claire’s mother, that Christian was her father, and that Jack and Claire were unwitting half-siblings. I hadn’t connected those dots myself, but the theory immediately made sense to me. When I interviewed Cuse that summer, he mentioned Christian Shephard, and I said, “And he’s Claire’s father, too, right?” Cuse looked like he was about to have a heart attack.
Alan Sepinwall, The Revolution Was Televised: The Cops, Crooks, Slingers and Slayers Who Changed TV Drama Forever