User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-10901795-20130722130637/@comment-6068707-20130723034832

It could be from the house of hades itself, or their could be someone along the way that mentions the prophecy kinda like how the Amazons mentioned a prophecy about someone taming Arion, AKA Hazel.

It could also come through the visions in the dagger. Or some one contacts the camp and has Ella or Rachel read a prophecy. But  I only said it could happen, only time tells.