Castle star Nathan Fillion admitted Saturday that he was quite shocked by this season's big twist.

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When Fillion first found out that new Castle showrunners Alexi Hawley and Terence Paul Winter were going to break up Castle (Fillion) and Beckett (Stana Katic), he was thrown for a loop. The actor spoke about it at a Paley Center panel for Dr. Horrible's Sing-Along Blog on Saturday.

"First of all, I asked them if they were high," he admitted, according to TVLine. "Second, they reassured me that what was going was they wanted to get back to a time when people were rooting for the couple, rooting for them to get together, to do something."

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Now, the show is essentially going back to where it started, with Castle and Beckett apart while he tries to win her over again.

"People had a desire, a wont, for them to fight for something," Fillion noted. As such, the star commends the writers for bringing back the show's original dynamic. "I think [the showrunners] did a really good job."

Ultimately, fans know that this isn't the average couple break up. Beckett wishes to protect Castle as she hunts down Bracken's (Jack Coleman) partner, an endeavor that could have deadly consequences. Luckily, the showrunners know the comedic lightness of Castle is what makes it so great in the first place, and that tone will continue even as this storyline unfolds.

"One of the things that Terence and Alexi are really big on, and I agree, is they don't consider Castle to be a drama," Fillion said. "It's never been much of a drama; it's far more a comedy with dramatic and heartfelt moments. And they wanted to bring it back to a time when it was funny, when it was great, when it was the lighthearted show that everybody fell in love with."

Castle airs Mondays at 10 p.m. ET/PT on ABC.

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