The Princess Diaries is a romantic comedy film in which Anne Hathaway stars as Mia Thermopolis, a socially awkward teenager who discovers that she is the heir to the throne of a small European country. The film follows Mia's journey as she navigates the challenges of royal life while trying to stay true to herself. Hathaway's charming and relatable portrayal of Mia endeared her to audiences, making the film a commercial success and launching her career in Hollywood.