Jean figured it out herself through her interactions with Venti and had it confirmed during Reunion With the Dragon when Dvalin addressed Venti as Barbatos. Diluc was also present during that scene and thus learned Venti's identity then as well, although from his lack of surprise, it is possib...
Fun Facts No.2 - Residents of the WildOfficial Genshin Impact HoYoLab Stormterror DvalinOfficial Miyoushe Chinese Post City of Winds and Idylls CD Set ArtworkGoogle DriveArt by Criin Event ArtworkSlime ParadiseMain article: Slime Paradise