How did Log Horizon members find out Tetra's real gender? Before the raid on Depths of Palm (Gold of the Kunie) in Susukino where Shiroe looks for full party members, Naotsugu and Regan find Tetra. Later on in the raid of Depths of Palm, Tetra joins (or is permitted to join) Log Horizon.

It seems that all members of Log Horizon, except Naotsugu, know that Tetra is actually male. How is that?
Shiroe learned Tetra's secret by intuition, but he left it up to Tetra to tell Naotsugu that he's a dude. I doubt Shiroe kept it a secret from anyone else but Naotsugu since Tetra only said that he wants to tell Naotsugu himself.