It grieves him to hear that. "Obi-Wan did as well." There's...emotion to be sure about that. But it's a tangled need of love, hate, resentment, longing, betrayal, grief, and more. Their relationship was strained and tainted by Vader's Fall but it hadn't been served. Damaged but not broken.

"Yes. It's much worse on the side of the Sith. Bane caused so much knowledge to be lost." Vader's voice trachea on a hunger there. Knowledge has always been his weakness. "There are so many mysteries within the Force."