Whenever Primus is seen travelling on his quest for the stone, he is alone ("primus" is Latin for "first"). Whenever Septimus is seen on his quest, he is accompanied by six servants, making a total of seven in his group ("septimus" is Latin for "seventh").
Miramax originally had the option on Stardust (2007), but after it expired, author Neil Gaiman felt uncomfortable giving up the rights to the film to just anyone. After turning down numerous directors and young actresses who wanted it as a starring vehicle, Gaiman finally gave Stardust (2007)'s option for free to Matthew Vaughn. This was largely due to the fact that Gaiman trusted Vaughn, both as a friend, and as someone "who stuck to his word", something Gaiman considers a rarity in Hollywood.
Matthew Vaughn had great difficulty in shooting the scenes at the inn to which Lamia (Michelle Pfeiffer) entices Yvaine (Claire Danes), Tristan (Charlie Cox), and Primus (Jason Flemyng), because there were very few occasions in which more than one cast member was available on any given day for filming these scenes. Consequently, there is a lack of wide shots and tracking shots containing several characters, and much use is made of stand-ins in the closer shots, to give the impression that all the characters were present.
The lead character's name was shortened from the book's Tristran, with an "r" between the "t" and "a," to Tristan, because Tristran was hard to pronounce quickly. However, there is one time it is said as "TristRan" instead of "Tristan." This is during the scene when Tristan remarks that Yvaine sometimes glows, when he suggests jokingly that the thing Stars do best is annoy boys called "TristRan Thorn."
After initial conversations between Producer Neil Gaiman and Matthew Vaughn about how to make the film, Gaiman found that Vaughn was most comfortable with all the action sequences and adventure bits, but needed help with the romance side of the story. To complement Vaughn's style and better capture all the aspects of the book, Gaiman introduced him to Writer Jane Goldman, and the two hit it off and wrote the screenplay.
The letter the scientist sent to Dunstan reads, "Dear Sir, Thank you for your inquiry concerning the existence of another world beyond The Wall surrounding your village. In our opinion, the hypothetical existence of such a gateway would run contrary to all known laws of science. Subsequently, in the opinion of my esteemed colleagues and myself, the idea may be safely dismissed as merely colorful rural folklore. I thank you again for your enquiry and hope that our conclusion will enable you to proceed with your life. Yours faithfully,"
In the original novel, the role of Lamia is actually a rather minor one. It wasn't until Michelle Pfeiffer signed on to the project that the role was greatly expanded to become one of the main characters.
The Princes' names all refer back to their place in the family: Primus, the first born (Primary), Secundus, the second born, Tertius, the third (Tertiary), and so on in that fashion. Likewise, Una the Princess, is the first-born daughter. This tradition come from Latin, as some Romans called their children after the order of their birth, though usually as a nickname, only sometimes being a given name, especially with daughters.
In the mural painted on the outside wall of The Slaughtered Prince pub, the victorious prince standing over the prince that he has slaughtered, has Peter O'Toole's face. The pub name, "The Slaughtered Prince," is a sly reference to the pub The Slaughtered Lamb in An American Werewolf in London (1981).
Ben Barnes (young Dunstan Thorn) was a fan favorite, and the preferred choice, for Tristan over Charlie Cox, as he was considered more attractive. Matthew Vaughn intentionally cast Charlie Cox, a then-unknown actor over big name actors like Orlando Bloom, as he wanted an actor who could play a dork, and easily transition into a suave and handsome gentleman.
For the scene where the "Caspartine" crash lands on the lake, the film crew traveled to Tenby, Wales to film the R.N.L.I. lifeboat (R.N.L.B. Haydn Miller). At the time, it was the first of a brand new class of lifeboat, with a brand new station. Someone on the production team had seen a photo of the splash the vessel made when entering the water from it's slipway, and felt it would be ideal to use the splash for the film (with the lifeboat edited out digitally). The studio made a one thousand pound donation to the R.N.L.I. (which is entirely funded by charitable donations).
During one of the sacrificial scenes involving the witches, a crocodile is used. A pig was originally intended to be the sacrificed animal, but Paramount Pictures insisted on another animal, like a crocodile, as it was not as offensive.
Charlie Cox, Sir Ian McKellan, Michelle Pfeiffer, Mark Strong, Henry Cavill, and Jason Flemyng all appear in superhero film adaptations. Pfeiffer played Selina Kyle, a.k.a. Catwoman, in Batman Returns (1992), while Strong played Sinestro in Green Lantern (2011). McKellan played Erik Lehnsherr, a.k.a. Magneto, in the X-Men film franchise, while Flemyng played Azazel in X-Men: First Class (2011). Cox plays the title character in Daredevil (2015), while Cavill plays Clark Kent, a.k.a. Superman in the DC Extended Universe.
The trivia items below may give away important plot points.
The Princes, when killed, are all shown to bleed blue blood. This is a joke hinting at their nobility, as those of royal heritage were said to have blue blood in their veins, rather than red. As the Princes are of royal heritage, they are literally "Blue Bloods". This may also have allowed the filmmakers to depict greater violence on-screen, while maintaining a lower age appropriate rating.
At the end, when Una tells Tristan he is the last surviving male heir, the spirits of the brothers float up and away. But one of the dots turns red and goes down into the fire, presumably Septimus, as he was the most evil of the brothers.
After confessing their love for each other, Yvaine and Tristan proceed to sleep in the same bed. Tristan was originally bare-chested in the scene, but it was considered to be too suggestive, so a shirt was digitally imposed onto Charlie Cox's chest area.