MAY CONTAIN SPOILERS

As Castle Season 5 came to a close, the ABC series’ titular author solved one big mystery not of his own crafting by getting down on bended knee and asking lady love Kate Beckett to marry him.

And while the bold move perhaps caught some viewers off guard — after all, things were starting to go south for the couple in the wake of Beckett feeling out an out-of-town job opportunity — Nathan Fillion‘s eyebrows were not among those arched.

“No, it doesn’t shock me that we were shocking people,” the actor shared with TVLine last week, as his Joss Whedon-penned/directed film Much Ado About Nothing began hitting theaters. “It’s not a shock for me.”

Neither was Fillion taken aback by the quite serious tone to the question-popping, as the finale’s closing scene purposely played out in a manner that seemed headed toward a break-up.

“It was important to me not to spoil it, not to telegraph where it’s going,” Fillion says of his alter ego’s approach. After all, he points out, “This is probably one of the more grown-up things Castle has done since becoming a father — and even in being a father, he’s not very grown-up about it. [But] fatherhood happens to you. Making a choice to be with someone for the rest of your life, that doesn’t just happen. That is an adult choice you have to make. That is some growing up you have to do. So I wanted to treat it as though it was a serious thing for Castle.”

All of which brings us to, you know, Kate’s answer. Although some fans have theorized that Fillion and leading lady Stana Katic went ahead and filmed Beckett’s response while there at the playground location — if only for continuity sake — the actor confirms, “No. We did not shoot the answer.” Nor does he know what it will be.

“We did that last day of shooting on a Thursday. Friday, I came in and did some looping … and then left town immediately [to] work in Canada,” he reports. As such, he maintained, “I have no idea, not a one. I’ve not had one email, not one discussion, not a phone call about where things are going, what’s going to happen. So I can’t even spoil anything by accident!” [SOURCE]