Be warned, if you have NOT watched last night's episode of The Walking Dead, "Killer Within", stop reading right now. There are massive spoilers below. Read on at your own risk.

The body count continues to pile up in Season 3 of The Walking Dead, with last night's casualty easily the most shocking of the entire season thus far. Sarah Wayne Callies' Lori, the wife of Andrew Lincoln's Rick Grimes, passed away, sacrificing herself for her baby's life. This episode was shot in June, which meant the actress had to essentially lie about her fate for five months. She revealed in a recent interview that the constant dishonesty was the hardest part about the whole process.

"It was the single hardest thing of this entire process, knowing that I had to [keep quiet] from the middle of June until the middle of November. And then I had to work on another project, [the film Black Sky]. I got onto that set and there were a lot of people who were fans of the show that were like, 'Aren't you shooting right now?' And I basically told them that every character this season has more episodes off than they've ever had, and the writers were kind enough to accommodate this schedule - all of which is true. But it was also deliberately misleading. It was by far the hardest thing. But [AMC] was very clear: You can tell your mom, you can tell your husband, and that's basically it. [Laughs] It was a real challenge. I think we were all very conscious of the ways in which Shane's death got out [before the episode aired]. And while it didn't diminish [Jon Bernthal's] performance, I think it diminished the experience of the audience watching it. So the publicity team at AMC said, 'Look, we're going to keep working like you are still the leading lady of the show for the rest of the season. And then when you die it's going to be crazy.' And it seems like that worked. To be honest, I can't believe it. I'm floored."

When asked if she thought her character's decision was selfish, she didn't pull any punches with her response.

"I think that's ridiculous. [Laughs] She's providing the most powerful symbol of hope and renewal that exists - which is this idea that life can go on and can grow, even in the midst of the end of the world. She was also losing about a cup of blood a minute. And if you can't deliver the baby and you can't stop the bleeding then she's dying one way or the other. As soon as the blood hit Maggie's hand Lori knows she's not leaving the boiler room. And if she dies and the baby dies then the baby turns. So then someone's going to have to put a bullet in that baby. She realizes that one of them could potentially come out of this alive or they could both die for sure. And given how hard Rick has worked to protect Lori and the baby, the greatest gift she can give him at that point is at least the success with the baby. He did it. He did it. He got her to term. He kept the baby alive."

She also spoke about being "banned" from the set during the scene where Rick (Andrew Lincoln) learns about his wife's death.

"Andy (Lincoln) asked me not to be on set. But I couldn't leave, so I was at base camp with the trailers. I could hear him screaming and crying [while shooting the scene]. I was sitting there with IronE Singleton [T-Dog] kind of going, 'Oh my God. This is horrible.' And then one by one as the scene ended they came back to the trailers to change and go home, and I put my arms around Andy. When he goes down the rabbit hole he goes all the way down. I put my arms around him and I was like, 'Look at me. I'm right here. I'm alive! Andy and Sarah are just fine. Rick and Lori are over, but Andy and Sarah are just fine.' [Laughs]"

The actress also spoke about her reaction to watching the finished scene for the first time.

"I thought it was brilliant. I thought it was brilliantly shot to have Carl strong and cold in the foreground and Rick collapsed. I know they shot it a bunch of different ways. There were a bunch of different ideas about how that scene could play. But it was beautiful because in some ways it's the apotheosis of Carl. It's this young boy having just performed a great act of both mercy and violence [against] his mother recognizing that dad's not going to be able to get me through this right now, so I'll be the strong one."

Sarah Wayne Callies revealed she did not regret getting to play a "walker" before her demise.

"The only regret that I have about that is that [Walking Dead special effects guru] Greg Nicotero has these amazing stylized posters made of the people who have left the show as zombies, and the one of Jon is phenomenal. And I asked him, 'Do I get a poster?! I want a poster!' And he was like, 'You didn't turn into a zombie.' But I remember Jon telling me that the zombie transformation is so hard. We spend the entire show hating them and running from them and trying to kill them. And to watch that transformation would be incredibly difficult. Greg has told me that they've had people weep in the chair. Some grown-up actors needed a scotch. It's an emotional transformation. And I think maybe I've had enough emotion already."

She is also looking forward to watching the show as a fan for the first time.

"I'm kind of looking forward to it [because] it'll be the first time I'll be watching without knowing what's going to happen. I get really easily scared, so I may have to watch from across the room with a pillow over my eyes for some of it. [Laughs] But they are phenomenal actors. Especially David (Morrissey). The stuff he's doing this season [as the Governor] is just blowing me away. One of my biggest regrets is that I don't get to work with him. We were both really looking forward to working together."

The Walking Dead Season 3 continues with "Say the Word" Sunday, November 11 at 9 PM ET on AMC.