User blog comment:CardMaster2412/Seven Half Bloods Parent and Identities/@comment-4354821-20110922020232

Another theory which i have said somewhere else. There is a possibility that out of the doors of death comes a old hero like Theseus or Jason or Hercules. Maybe they could be the seventh. Either way I don't think we will know about the seventh after the son of Neptune, I think Rick will save that for Book 3