Kevin Bacon, Connie Nielsen

The Following blindsided viewers with a game-changing twist last week, exposing Lily Gray (Connie Nielsen), who had been positioned as a new love interest for Ryan Hardy (Kevin Bacon), as a devotee of Ryan's nemesis, Joe Carroll (James Purefoy).

"It's really hysterical because I've been unable to tell anybody, even my kids," Nielsen tells TVGuide.com about her new character. "I've received so many text messages. My whole family and all my friends have been like, 'I knew it! I knew it!'"

Exclusive Following sneak peek: Ryan figures out the reason behind Lily's betrayal

In some ways, Nielsen says, having to stay mum about Lily's true motivations helped her identify more with the character. "It was just such a great thing to be able to play as an actor," she explains. "I just absolutely had so much fun positioning this manipulation, the way psychopaths or people living on the psychopathic spectrum actually do it. They're so detached and methodical in the way that they snow people into believing that they're normal, nice people with morals and with empathy, when in fact they have no such thing and they're just mirroring your expectations of a normal behavior. And it was just so interesting to get to play that with Kevin Bacon, for example. We both knew that it wasn't the truth ... and I remember having these thoughts as my character, thinking, 'What if this were not pretend? Wouldn't that be nice?'"

Now that she's at liberty to talk about Lily in detail, Nielsen says that the art gallery owner will emerge as one of the biggest threats this season. "I think it's safe to assume that Lily is very, very, very intelligent, that she has very few limitations put on her," Nielsen warns. "She is very, very wealthy and can do an enormous amount of things. And she's not burdened by empathy or guilt. That sets her free to be a lot of different things and do a lot of different things."

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So how did Lily — who was presumed to be a victim of Carroll's followers after the brutal subway attack in the season premiere — sneak under the FBI's radar, even passing a thorough background check with flying colors? Nielsen says her back story will be explained in full, but hints that it's actually not as complicated as viewers may think. "I think that this happens all the time, where people realize that the guy who was living next door was some psychopath monster, and he seemed so nice," Nielsen says. "The police had no priors on him, and there was no indication except for things that you can only find out in hindsight. ... It just seems like most of the time when it comes to this type of personality disorder, you just don't see that coming until it's right in front of you."

And of course, last week's discovery sends Ryan Hardy back to the drawing board as far as his love life is concerned. Nielsen doesn't deny that there was a spark between Lily and Ryan, but says with conviction that it was all part of Gray's ruse. "I don't think she has any guilt whatsoever," Nielsen says. "I do think [she has] a little regret, however. I do think that she kind of liked him a lot. But she also knows who she is and what she's really like, so she also knew that that wouldn't be an option."

Will Lily emerge as the de facto leader of Joe Carroll's new cohort of followers in New York City? It certainly seems that way, with twisted twin Luke (Sam Underwood) referring to her as "Mom" last week. And while it's unclear at this point whether Lily is Luke and Mark's biological mother or just a den mother figure, Nielsen says her fierce desire to protect them isn't dependent on DNA. "That is one of the things I really have enjoyed playing with," she says. "People with certain types of disorders, it would seem they would not know how to respond in a natural way with regard to family, and yet you will see them be obsessed about their child. ... I think that she definitely loves them in that unconditional way."

Fans of the show shouldn't assume they know where Lily's story line is heading, according to Nielsen. Last week's Lily-related twist is just the first of many this season. "What you think is about to happen is not what [her] back story is," she teases. "Every episode is going to be so full of switches and turns and things you just don't see happening. It's going to be a ride."

The Following airs Mondays at 9/8c on Fox.