This 'spoiler' is based off of rumors that I've read online, so it's technically not a spoiler as it really would be defined ...
Boone & Shannon are brother & sister, but only by marriage, and used to be a couple ... it's why there's so much tension/animosity & whatnot.
My guess is that they were fucking before their parents (say, his mom & her dad, or vice versa) hooked up and thus their relationship had to end.
We'll find out in 7 hours & 45 minutes ... well, it'll be tomorrow for me, I'll just be taping the show & watching it tomorrow night instead. But I digress ...
I knew something like that was going on.
But can't step's still date?