‘Firefly” aired for only one season 10 years ago, but Nathan Fillion still hasn’t gotten over it.

“It was the best character I ever played,” Fillion told The Post. “The best dialogue to ever come out of my mouth was on that show.

“It was my first time truly being in love with my work,” he says. “It’s the bar to which we compare every job.”

The fans aren’t over “Firefly,” either. More than 10,000 of them lined up for the 10-year reunion of the sci-fi cult classic at San Diego Comic Con this past summer.

Behind the scenes there, Fillion joined “Firefly” creator Joss Whedon and castmates Sean Maher, Summer Glau, Adam Baldwin, Morena Baccarin, Alan Tudyk, Gina Torres and Jewel Staite to film a reunion special airing tomorrow on Science Channel (10 p.m.).

“Firefly,” which aired on Fox in 2002, was set in 2517 and revolved around the renegade crew of a spaceship.

Fans will see their favorite space cowboys reminisce about how it all began — from the crush Glau had on Fillion at auditions to Whedon’s first impressions to the show’s cancellation, paired with clips from the series.

Whedon went on to write “The Avengers,” Baccarin stars in the Emmy-winning “Homeland” and Fillion in the ABC hit “Castle.”

But Fillion says he gets as many fans coming up to him yelling “Capt’n” as “Castle.”

(His “Firefly” character was called “Cap’n Mal.”)

“The ‘Firefly’ fans, they’re with you for life. Joss Whedon fans are with you for life,” he says.

“Certainly a ‘Firefly’ fan will mention ‘Castle.’ ‘Oh, but we like ‘Castle,’ too!’ They’ll throw that in there for you — throw you the ‘Castle’ bone.”