[@Grnmachine] He wouldn't be able to deny it, nor would he think it is a prank for many reasons. The first is that he has had that mark since he was born and there are only marks on the chosen. Second the disciples of the water goddess would be checking in on him multiple times throughout his life, not keeping it a secret at all. Third, the previous water chosen would also check in on him a lot throughout his life. Fourth, everyone and i mean everyone would know his family and him. They'd know he was the chosen of water so there is no getting around it being mentioned to him multiple times by multiple people. Plus there are occasionally meetings of all chosen ones which include previous and the new ones start going too about at the age of 5.