ORLANDO, Fla. – Nathan Fillion is the star of a popular TV show – “Castle.” And every show has its share of fanatical fans. He was on a soap opera for years, whose enthusiasts take “fan” to a “whole different level.” But that’s nothing compared to the devotion that comes from a TV show (“Firefly”) he briefly did with Joss Whedon (“Buffy the Vampire Slayer”/“The Avengers”).

“Joss Whedon fans never go away,” Fillion says. “They will follow you from project to project, supporting you every step along the way. … I don’t try to understand it. I just enjoy it.

Whedon knows it, too. When the 48-year-old phenom puts his name on a horror picture (“Cabin in the Woods”), he brings an audience to it that might not otherwise go. And when he takes on a major comic-book film franchise like “The Avengers” and knocks it out of the park, at least part of the audience is guaranteed to smugly cross its arms, look around the theater and say, “We told you he was special.”

But can Whedon and his on-screen muse, Fillion, lure that elusive fanboy audience into watching a Shakespeare movie? There’s the rub, as the Bard’s marketing department might say, behind Whedon’s low-budget but sexy take on “Much Ado about Nothing.”

Whedon joins some of the screen’s greatest storytellers – Welles and Olivier, Polanski and Branagh, filmmakers who love Shakespeare and who, as Whedon puts it, “try to get the audience to see what you see in it.

“Everybody who loves Shakespeare wants the chance to step up and say, ‘This is what it did for me.’ It’s a little affirmation for Shakespeare. He touched me, and he’ll touch you.’”

And if the audience comes, all the better. “Nobody ever does Shakespeare for the screen for any other reason other than they love it,” says Whedon, lowering box-office expectations for the film. “In high school, we’re forced to do it. When you’re an adult, if you’re doing it, it is out of love.”

Whedon and his wife, Kai Cole, would host Sunday “Shakespeare” brunches in the big, rambling L.A. home that Cole designed. They’d invite many of the Whedon repertory company of actors he’s worked with on TV, “have some mimosas and perform a play,” Fillion recalls. That combo really worked on the comedies, and “Much Ado About Nothing” in particular.

“The drunker we got, the better the play went,” Whedon jokes.

The writer-director, known for being fiercely loyal to his actors, had been longing to find a way to showcase his friends Amy Acker (“Angel”) and Alexis Denisof (“Angel,” “Dollhouse”). That became a project that Cole convinced Joss to film as a “soul-restoring” way of spending his break between filming “The Avengers” and settling down to edit it. In just 12 days, over two weekends, using actors such as Acker, Denisof, Clark Gregg, Fillion (who plays Dogberry, the comical constable) and Ashley Johnson, in modern dress and in a perfectly modern house, they transformed “Much Ado” from a mimosa-soaked revel into a movie.

“This was his version of a vacation,” Fillion says of Whedon. “He loves the language, the stories, the themes. … I think high school teachers will rejoice at this film, because it proves that anybody can enjoy Shakespeare. I was one of those kids who tuned out whenever somebody said ‘Shakespeare.’ ”