[It was a deductive guess. Lan Wangji recognizes the fashion of their clan and their mannerisms. It's the same variant of his other double, and with their similarities.]

Lan Xichen? My brother. [He isn't certain if this is the brother who knows him and grew up with him.] It's so good to see you. I am glad. Are you well in good health?

Yes, I am Lan Wangji. And yet...perhaps not? You dressed differently. You dressed like the other Lan Wangji, I met a while ago. I think that one is your brother.