User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-3146930-20130611215552/@comment-6064271-20130612233938

well, maybe you are thinking of the great prophecy, Chiron promised the gods on the River Styx that he would not tell Percy or anybody that was a child of the big 3 what the great prophecy said. Though Annabeth told Percy part of the prophecy because percy asked her to and that was all she knew at the moment. That the children of the Big 3 are the most powerful demigods and that the next one to reach 16 will decide the fate of olympus.