Damian doesn't know how it happened. All he knows is he woke up and his life was different. It might be some Flashpoint thing, or universal change, he doesn't know. The most outstanding difference was his mother, who is no longer Talia but you and his father married you, surprisingly happily.

"Uh so...Mother, how did you meet Father?" Damian asks. The best plan is to ask you questions, to see how the hell you turned out to be his biological mother and not Talia.