What is the name of the book after The Titan's Curse?

The fourth book in the 'Percy Jackson and the Olympians' series by Rick Riordan following 'The Titan's Curse' is 'The Battle of the Labyrinth'. The fifth book is the 'The Last Olympian'.

There is no sixth book in Percy Jackson. However, there is going to be a new series which is called Heroes of Olympus.

Percy, Annabeth, and Grover do appear in this series, but they are not the main characters. The first book in Rick Riordan's new series will be called The Lost Hero