Although the film was written by Ben Best and Danny McBride, the dialogue is heavily improvised. Director David Gordon Green said there was never a script used on-set. Only the plot outline and written notes were used.
The premise for the movie evolved from a frivolous game David Gordon Green and Danny McBride used to play to while away on film sets. Each would take turns in suggesting a title for a film, and the other would try to concoct a viable storyline. When the title "Your Highness" was put forward, the premise was, "It's about a Prince who gets stoned and fights dragons."
Natalie Portman admitted she only did this movie because there was some uncertainty if Black Swan would get green-lit by a major studio. She signed on to this film for a paycheck, and use it to help finance Black Swan herself, should the need have ever risen. However, Black Swan got green-lit, and went underway fairly easily, and Natalie got stuck doing this film having already signed on.
The name of Belladonna (Zooey Deschanel) could be taken to mean "beautiful woman" in Italian. However, belladonna is also an extremely toxic plant (Atropa belladonna, a.k.a. "Deadly Nightshade") used in ancient and medieval times as an aphrodisiac, a hallucinogenic, and a poison. Witches were said to use belladonna to enable them to fly.
For the green band (appropriate audiences) trailer a shot of Natalie Portman's back (that was also used unaltered in the red band trailer) was digitally altered to turn a thong into a more substantial and less revealing garment.
A possible sequel has not been ruled out, and Danny McBride may return as Thadeous. Natalie Portman may or may not return as Isabel, and James Franco is not likely to return as Fabious, because he disliked the film. However, due to the film only earning 24.8 million dollars worldwide on a budget of 49.9 million dollars, a sequel is highly unlikely.
Isabel (Natalie Portman) could had gone on to her own spin-off movie. But, due to negative reviews from critics and poor box-office results, a possible spin-off film, which focused on Natalie Portman's character, never came to consideration or realization.
The trivia item below may give away important plot points.
The ending which Isabel convinces Thadeous to go with her to slay the witch, which Isabel will be free of her chastity belt hinted at and left it open for a sequel. But, due to poor Box-Office results, a sequel never happened.