The Princess Incognito series and the book Awful Agatha are written by N. J. Humphreys.
The series is a humorous adventure chapter book about a princess named Sabrina who is forced to live a normal life in a school while hiding her royal identity. In Awful Agatha, one of her main school rivals is Agatha, who dislikes Sabrina and often creates trouble for her, adding comedy, conflict, and school-life drama to the story.
It is written as a prose chapter book (not a graphic novel) with short chapters and simple language, making it easy and engaging for young readers. The series is best suited for primary upper readers (around Grade 3–6 / ages 8–11), especially children who enjoy funny school stories, secret identities, friendship drama, and light adventure plots.