During his tour for The Sword of Summer, Riordan announced his next project, a five part series about the god Apollo. The series will be about how Apollo has been turned into a human because Zeus is angry with him. He becomes a 16-year-old mortal boy in New York City with absolutely no powers. He has a lot of enemies and only a few friends — friends who spend their time at Camp Half-Blood.
Riordan referred to this series as "the capstone on Percy Jackson's world", so that by the end of it, all of the major characters from both previous series would be revisited. 
The first preview of the new series was shown in Demigods & Magicians on April 5, 2016.
- The Hidden Oracle - May 3, 2016
- The Dark Prophecy - May 2, 2017
- The Burning Maze - May 1, 2018
- The Tyrant's Tomb - October 2019