The song, "Your Crowning Glory", was the first time Julie Andrews had sung in public or on screen since she had throat surgery in 1997. She reportedly nailed the song on the first take, and brought tears to the eyes of the crew present.
In the beginning scenes when Princess Mia is explaining what has gone on since the first movie she says that she and Michael have broken up and he is now touring with his band. Robert Schwartzman declined to do the sequel in order to focus on his band, Rooney, which was touring the country at the time the movie was being made.
At the royal garden party, Princess Mia asks a guest how her three grandchildren, Lily, Charlotte, and Sam are doing. Those are the names of director, Garry Marshall's three grandchildren. The guest was Garry Marshall's wife, Barbara Marshall.
Julie Andrews loves fresh flowers, and convinced Garry Marshall to use only real flowers in the arrangements inside Rinaldi Castle. During the filming, she was constantly adjusting the arrangements, removing dying blossoms, etc. The centerpiece of the kitchen table (in the scene where Nicholas tops his chocolate mousse) got switched from a large piece (as seen in the background) to the cluster of small flowers seen in the final cut - the original arrangement got in the way of the filming.
Sofia Loren is in the birthday party scene when Raven Symone taps Anne Hathaway on the back while the latter is sampling the cake frosting. Seen right between and behind the two, wearing glasses and gold dress.
In the beginning of the movie, Anne Hathaway flings her bracelet to the palace guard, and he says "It happens all the time," which was an allusion to Julia Roberts' character flinging her escargot to the same person in Pretty Woman (another Garry Marshall directed film).
Lord Crawley and his identical twin brother (who don't get along) tersely acknowledge each other by their first names, Jerry and Dean. This is a reference to Dean Martin and Jerry Lewis, who were the most successful comedy team of the 1950's, yet were known to have had several heated arguments late in their joint career. They finally split up amidst a great deal of bitterness in 1956 and didn't speak to each other for twenty years.
At one point, Joe warns Mabrey to leave Mia alone, noting that he has "diplomatic immunity in 46 countries, including Puerto Rico." Hector Elizondo was born in New York, but his parents emigrated from Puerto Rico.
In the parade sequence with the orphans, in the top right corner, the marquee of the Genovian National Theatre indicates a production of "Wrong Turn at Lungfish" is being staged. This play was co-written by Garry Marshall and Lowell Ganz. This was also the play in which Kathleen Marshall made her off-Broadway debut in NYC.
In the Genovian Independence Day parade, the announcer introduces the Mertz marching band directed by Lucille Charmical. These are names from I Love Lucy, which Princess Mia later confesses to Chris Pine's character is a favorite of hers.
Elizabeth Gudenrath (as Beth Anne Garrison) is seen as Princess Mia's Princeton friend, Anna, in Princess Diaries 2 the Royal Engagement (2004) and previously portrayed Anna of Princess Diaries (2001) cheerleaders Lana, Anna, and Fontana.