Acclaimed TV drama ... Stana Katic as Detective Kate Beckett and Nathan Fillion as novelist Richard Castle. Source: Supplied

The 43-year-old Fillion is in one of the world’s most popular TV shows, Castle, but has none of the problems that come with fame.

You never see Fillion trailed by paparazzi, or embroiled in scandal, and his private life is kept under wraps.

Perhaps that is because Fillion, who plays mystery novelist Richard Castle opposite Stana Katic’s Detective Kate Beckett, spends 12 to 14 hours a day filming.

It is those long hours that have kept fans wondering how many more years Fillion will commit to Castle.

There are only occasional glimpses behind the scenes. A year ago, news emerged that Fillion was a no-show on set, supposedly because he was locked in a contract dispute with network bosses over his desire to move to a four-day work week.

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King of the Castle ... Actor Nathan Fillion. Source: Supplied

It was also reported that Fillion was upset that Katic was getting too much attention and screen time.

The actor is reportedly in a relationship with Spanish beauty Christina Ochoa, though he remains tight-lipped about his personal life.

“I was talking to a friend the other day who described my level of success as ‘perfect famous’,” Fillion says on a break.

“I don’t have to wait in long lines at the DMV (Department of Motor Vehicles), I can have dinner with friends in a restaurant, and at the same time the paparazzi aren’t following me. I think I can credit the long hours we’re on set for that.

“I don’t have any time to get in trouble.”

Fillion burst on the scene in 1994 playing Joey Buchanan in soapie One Life to Live. After a role in Saving Private Ryan he linked up with producer/director Joss Whedon (The Avengers).

The pair’s TV projects included Firefly, with Fillion playing Captain Malcolm Reynolds, and Buffy the Vampire Slayer (as Caleb). In 2007, he landed the role of Dr Adam Mayfair in Desperate Housewives.

Working on Castle requires sacrifices ... TV show’s star Nathan Fillion with co-star Stana Katic (Kate Beckett). Picture: ABC / Matt Kennedy Source: Supplied

The first episode of Castle aired in March 2009 and immediately hit a sweet spot with audiences weary of intense forensic-based crime dramas such as CSI: Crime Scene Investigation. The audience has grown steadily, from an average of 10 million in its first season to 13 million today.

“Even though Breaking Bad has ended, for the most part shows like CSI and NCIS are typically very heavy whereas we are a show that doesn’t take itself especially seriously,” Fillion says. “I think we lean a little harder to the lighter side of the characters and to their relationships.

“You can watch the show with the kids, the entire family. The older ladies like me because Richard Castle lets his mother (Susan Sullivan) live with him so they have a soft spot for Castle.

“There are also plenty of people watching Castle who have never heard of (past shows such as) Firefly. It is wonderful.”

The sheer number of hours on set is Fillion’s main gripe.

He usually arrives at the studio before 6am and filming often doesn’t wrap until well into the night.

“In this environment we’re removed (from the hype),” Fillion says. “We’re kind of locked in here. It seems a little insular. It seems a little confined at times. Thankfully we get to go on location occasionally.

“It’s not a glamorous life. It is a bit of a sacrifice.”

Castle, Universal, Monday, 9.30pm

Intimate moment ... Castle stars Nathan Fillion and Stana Katic. Picture: Channel Seven Source: Supplied