Complex sentence: In the end of the book, Luke who is also invincible from bathing in the River Styx stabs himself as a result killing himself in order to destroy, but not kill, Kronos and therefore save the Olympians.
Split into simpler sentences: In the end of the book, Luke who is also invincible from bathing in the River Styx stabs himself. As a result, he kills himself in order to destroy, but not kill, Kronos and therefore save the Olympians.