I have noticed every single time I give Blackfyre to a bastard, and if they change dynasties, if I grant independence, they have every single time attempted to press their claim on me, and their children as well. IDK if it was just a coincidence that every time it happened to me or not, but I would say there is a high probability you will create some pretty nice Blackfyre Rebellions. I usually end up with a lot of vassals declaring for the Blackfyres, so it makes it a nice challenge. If you want to create a challenge, make sure to also give the bastard a dragon egg, you'll end up with a lot of Dance of Dragons wars
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