It's their last day of filming in Hengdian when the secret comes out.

"That? That's your confession?" Yibo's toppled onto Xiao Zhan's side and is clutching his shoulder, trying not to fall over. "That's pathetic!" "Oh, what, you can do better?" Zhuocheng is pretty flushed and there's a challenge in his voice that Yibo just can't walk away from. "Hell yeah, I can. Hit me, Yu Bin." Yu Bin cheers and refills Yibo's shot glass. "All right!" Yibo downs the shot, gags only slightly, and says, "Everyone! I'm a fucking virgin!"

Xiao Zhan hears about it from Yu Bin, which probably should've been the first warning sign.