Photographer Brian Bowen Smith directs Castle stars Stana Katic and Nathan Fillion for their TV Guide Magazine cover shoot.

"The kiss offered them an opportunity to taste each other's prowess," says Katic. "For Castle to find Beckett's inner tigress. Roar!"

"In Beckett, Castle sees she's a very intelligent woman," says Fillion. "He's attracted to her intelligence and to the fact that she's an authority figure."

"I don't think Beckett uses people," says Katic. "There's an element of the character that we can unveil through a relationship — her romantic side, her romantic vulnerability, and her sensuality. You can't show that with the boys in the precinct."

"I think Castle is nearly complete, but he's got this little sliver of him that needs to be filled, and that's Beckett," says Fillion.

"I think they're great friends," Katic says of Castle and Beckett. "I think that she sees a partner in him and she loves his sense of humor."

Of Castle and Beckett's famous kiss, Fillion says, "We jumped right into it. If somebody asked you to do a zip line into a raging river, there's gonna be some safety issues involved. If it's a kiss, we've all done it. I think we all pretty much know what we're doing by now!"

Be sure to pick up this week's issue of TV Guide Magazine featuring the Castle cover stars on newsstands now!