Thanks. I think in a Starwars rpg, it would be fair to assume that every player at the table probably knows this twist. So if the DM tried to make this a big reveal, you would find yourself in a similar situation. At the odd chance that one player at the table doesn't know the twist, there is a high likelyhood someone else will blurt it out.
I think a DM is best advised not to incorporate plot twists from widely available books or movies, if they want them to be a surprise. Also, don't call your npc Shadowmantle.