1. It was Anne Hathaway's first feature film.
She starred in a TV series called Get Real the previous year, but The Princess Diaries was Anne's big break. As you know, she then went on to become one of Hollywood's most in-demand actresses, starring in Brokeback Mountain, The Devil Wears Prada, The Dark Knight Rises, and Les Misérables, for which she won an Oscar for Best Supporting Actress.
2. But the movie did limit Anne's options for a while.
"After Princess Diaries, I was labelled a good girl," she told Glamour. "For the first eight years of my career I had to fight to get any other kind of job." In another interview with the Huffington Post, she said, "It was hard to get into rooms to be taken seriously for roles that weren't princesses, so I think partially that was why I've tried to have as big a range as I have."
3. Another actress almost got the part of Mia Thermopolis, but director Garry Marshall's granddaughters convinced him to cast Anne.
Liv Tyler was reportedly in the running to play the quirky princess, but while watching the audition tapes, Marshall's granddaughters liked Anne the best because of her princess-like hair.
4. Both The Princess Diaries and Mary Poppins were filmed on the same soundstage on the Walt Disney Studios lot.
Julie Andrews starred in both films 37 years apart, and Stage 2 was formally named the "Julie Andrews Stage" in 2001.
5. Parts of the movie were inspired by author Meg Cabot's own experiences after her father died and her mother began dating her high school teacher.
On her website, Meg writes that she always had a "thing" for princesses and as a little girl she insisted that her real parents were a king and queen—and thus, the idea for The Princess Diaries was born.
6. In the scene where Mia and Lilly are hanging out on the bleachers, Anne fell in an unscripted moment, but Marshall loved the take so much he left it in the final cut of the movie.
Now that's talent!
7. Julie Andrews is the reason why Genovia is famous for its pears.
Marshall asked Julie what the fictional country would be known for; she suggested pears on a whim and he ran with it. "The next thing I knew the set was just dotted with fake pears and pear statues," she said in an interview.
8. Hector Elizondo, who played beloved limo driver Joe, and Larry Miller, who was eccentric hairdresser Paolo, were both in Pretty Woman, directed by Marshall 11 years prior.
As The Princess Diaries launched Anne Hathaway's career, Pretty Woman is often credited as the movie that made Julia Roberts a star.
9. Marshall also included another nod to Pretty Woman by including the same actor reciting the same line.
After Julia Roberts accidentally flicks escargot across the room in Pretty Woman, a waiter watches the snail fly and says, "It happens all the time." That actor, Alan Kent, appears again in The Princess Diaries after Anne Hathaway breaks a glass during a dinner scene, and repeats the same line.
10. Mia's love interest Michael was played by Rooney frontman Robert Schwartzman.
His real-life bandmates make an appearance in The Princess Diaries as Michael's fictional band Flypaper. Robert also acted in The Virgin Suicides, directed by his cousin Sofia Coppola. His brother is actor Jason Schwartzman, who used to be the drummer for Phantom Planet, and their mother is Talia Shire, who played Connie in The Godfather.
11. While she didn't get to keep the tiara she wore in the movie, Disney gifted Anne her own tiara after filming wrapped.
She also said that the movie tiara was very heavy. "It definitely takes some getting used to," she told Access Hollywood. "It gets old after five minutes."
12. Anne only auditioned once for the role of Mia Thermopolis, during a 26-hour layover in Los Angeles on her way to New Zealand.
She asked to audition for roles during her layover and cited Pretty Woman being one of her favorite films as the reason she wanted to work with Garry Marshall. "At some point of the audition I got really nervous and fell out of my chair, and I think that was what he was most impressed with," she said.
13. The movie was originally going called The Princess of Tribeca.
In the Princess Diaries books, Mia lives with her mother in New York City, but for the movie, their hometown was changed to San Francisco.
14. Whitney Houston was one of the producers of the movie.
Yes, that Whitney Houston. She also went on to produce The Princess Diaries 2: Royal Engagement and the classic Disney Channel original movie The Cheetah Girls.
15. One of the cats who played Fat Louie was actually owned by Anne.
A total of four cats played Mia's favorite feline, each one with his own special skill.
16. The picture of Mia's deceased father that's shown in her room is Anne's actual, and very much alive, father.
Her dad also played Mia's father for the short time he appears in the film.
Follow Lauren on Twitter.