[Gabriel had just opened the caravan door, but now he goes very still and half-looks over his shoulder. Because he knows that feeling. Protecting brothers, even though they don't deserve it. For a moment he doesn't say anything, but then:]

Lucifer asked me to leave with him, you know. Way back when. I said no. And then I promised not to tell Michael he was planning to leave.

[And then Lucifer had attacked his brothers, murdered Metatron, and threw Heaven into war. Because Gabriel had protected him.]