Victor_Vaden
I may be wrong, but I'm pretty sure nobody except the Sect Master and one of the Guardian elders know about Arthur's identity as prince and that he has a mask on. Was the revelation of his identity and taking off his mask skipped?
Before Arthur came to the sect, the Emperor had already contacted the Sect Master to keep it a secret until Arthur left. The Grand Elder knows because of Old man whitebeard. No one else knows. But after Arthur's disappearance the elders and the sect needed an explanation on his absence and it will later be revealed.