The Princess Diaries by Meg Cabot

The Princess Diaries is about a normal girl that finds out after 15 years that she is a princess. Mia is not like other girls that wish to be princesses. She just wants to be a normal person with a normal life. But she has to. It's in her blood. To be a princess, she has to do a couple things. She has to make sure that nobody at her school finds out about her being a princess, she has to go to princess training with her grandmother, and act like a princess at the same time. She faces a couple challenges on the way. She was almost going to give up the throne, but she stopped herself and continued to be the princess. At the end, she became the Princess of Genovia.