I don't actually know if this counts - it probably doesn't, as the whole point of it is to be spoiled, seeing as how it's nearly thirty years old - Rose of Versailles. Seeing as how a few of the cast were prominent real-life aristocratic figures during the French Revolution, you know they're gonna die right off the bat - and even the narration in the comics and anime immediately acknowledges it for the sake of creating tragic character development.

But it seems to be pretty much the initiation in fandom, in that you talk openly about how the main characters (fictional) also die horrible and tragically in the finale as well, even if you haven't seen it. (In fact, the last episodes were just released on bittorrent with this as the main advertisement!)