Now that Castle‘s Rick and Kate have (finally) coupled, don’t worry about some silly push-and-pull thing as they grapple with their new closeness.

Visiting TVLine’s Comic-Con suite, Nathan Fillion assured me that while Castle will still be a “pain in the butt” and Beckett (played by Stana Katic) will still at times be “emotionally unavailable,” this new couple is “in it, to win it.”

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As for the dreaded M-word – Moonlighting – Fillion notes that versus the fall-out of the David/Maddie hook-up, Castle‘s writers “have been very clever in not treating this as an ending [but] a protracted beginning. Now ‘it’ can finally start.”

That said, Fillion teases new “problems” to come out of “it,” and he also reckons the Beckett’s Mother’s Murder storyline will keep chugging, if only because “it is such a wonderful locomotive that keeps things moving.”

So then what to make of my reporting on the casting of a senator and Vice President of the United States for Season 5…? Fillion’s reaction to that, and a bit of light he seemingly (perhaps) sheds on it, is quite juicy.

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Also in this video: Fillion weighs in on Friday’s uberemotional Firefly cast reunion and gives the latest odds on a Dr. Horrible sequel.