[It's obvious that his discussions of Credo have been in the past tense. So he's fully expecting the question. It occurs to him then that he doesn't know how much Vergil knows about the Fortuna disaster. Nero hasn't spoken of it at all, but he'd referenced hearing some of it from Dante.

He counts on that being enough for right now.]

When they found out I was part demon... he turned on me. Tried to capture me on Sanctus' orders.

[He pauses to collect himself for the rest.]

Then he tried to save me and Kyrie. Sanctus murdered him. And I couldn't do a damn thing.