Starkiller wasn't stunned or shocked often. Though that information he was delivered made the young man stop in his tracks. This Jedi, trained his master, Darth Vader. His master, was a Jedi previously... trained and guided by the Jedi council.
Then he fell? Was it falling? There was so many questions in mind regarding around these facts. Starkiller looked to the ground while he contemplated his role, his purpose suddenly.
Then he caught up in stride with the Jedi. "You will train me." Starkiller confirmed. If he was to help his master over throw Sidious, he needed to be the best. To be the best, this specific Jedi was the path. "With your help, I will be able to destroy Sidious once and for all." And rule with his master, but that wouldn't be said to this man.