Castle Season 5: Behind the Scenes With Nathan Fillion, Stana Katic, and Guest Star C. Thomas Howell (PHOTOS)

C. Thomas Howell is the latest actor to join the laundry list of Castle guest stars who can't resist snapping a behind-the-scenes picture with Nathan Fillion. And we don't blame him! Have you seen how good Castle's main man looks in the first official Season 5 promo pic?

"On the set of Castle with @NathanFillion!" Howell tweeted on August 24. "Great guy... Cool show!"

But it wasn't just the geek god Howell wanted for his online scrapbook. The Southland actor also managed to snag the lovely Miss Stana Katic for a quick on-set photo op.

"Hangin' with @Stana_Katic," he wrote.

No word on Howell's role, but we know his character will appear in Season 5, Episode 4: "Swan Song," airing on October 15. 

Are you excited for C. Thomas Howell's guest spot? Tell us below!