That’s just it. Pretender and class idea’s like it are intrinsically tied to the King role. You can’t have an election end in someone being elected but not have the King role get involved at some point, so you are going to have to deal with the fact that a successful Pretender will end up being King at some point.
Unlike with Scorned and Inquisitor this isn’t inherently bad, and unlike with Fool the Pretender is still alive.
So no it’s not after the fact. The Pretender King is DURING the fact. That’s when the Pretender is making her move, she’s in power and now she’s using it and it’s up to the BD to catch that (or think they did if it’s a BD King).
It’s like if Scorned won the second her target is upped. Yeah she convinced people that they were suspicious but how she has to get them to follow through with that and actually execute them.
Sure you’ve became King but so what? Why should BD care about a Pretender King? If she hasn’t outed already why would she not do so now and then be a boring Kingmaker that no one wants when she could be an interesting psudo-EK that potentially no one suspects, and thus acts as a way for elected Kings to be more easily pushed by scum when a Pretender doesn’t spawn.