If you've ever wondered what 'Castle' star Nathan Fillion does on his days off, wonder no more. He apparently makes movies in secret with his erstwhile 'Firefly' boss, Joss Whedon.

According to 'The Wrap,' Whedon adapted, cast and filmed a new indie version of William Shakespeare's 'Much Ado About Nothing' this summer without anyone finding out until after it was finished.

A website went up Sunday night announcing that principal photography has been completed on the guerrilla filmmaking project, which is lightheartedly described as "A Film by Joss Whedon Based on a Play."

The cast is a veritable smorgasbord of Whedon faves: As well as Fillion there's Amy Acker and Alexis Denisof from 'Angel' and 'Dollhouse,' and Sean Maher ('Firefly'). Although it could all be an elaborate hoax, we're already loving the idea of Acker and Denisof re-teaming to tackle the roles of reluctant lovers Beatrice and Benedick.

Frequent Whedon collaborator Shawna Trpcic, who was the costume designer for 'Firefly,' 'Dollhouse' and 'Angel,' Tweeted Sunday night "Oh, it's real. Very. Very. Real." Maher backed her up, Tweeting "I promise you it's the real deal and we're VERY excited about it!"

It's not the first time 'Much Ado' has been adapted for the big screen. Kenneth Branagh assembled an all-star cast including Denzel Washington, Keanu Reeves, Kate Becksinsale and Emma Thompson for his successful 1993 version.

The play has also been adapted for TV several times, the most recent being a BBC version starring Damian Lewis ('Life') and Billie Piper ('Doctor Who').

The comic tale of two pairs of lovers, Benedick and Beatrice, and Claudia and Hero has been a perennial fan favorite since the 17th century. And it's not just earthlings who love the play: There is also an official Klingon version.

'Doctor Who' stars David Tennant and Catherine Tate burned up the London stage as Benedick and Beatrice this past summer.