Vader survived the second Death Star, and has since devoted himself to wiping out the slave trade on the Outer Rim. When Ben doesn't want to go and be trained as a Jedi, the first person he runs to is Granddad, who is quite willing to give the kid a bit of training while fighting slavers and trying to free the slave planets. Vader's survival is a major secret, however, so Snoke still tries to get at Ben through his well-known hero-worship of his grandfather. He wasn't expecting Vader himself to be there when they finally set up a meeting.
Bonus points for:
- Ben's been following Vader like a duckling since he was very young.
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