AJ Langer, Paul Adelstein

[Warning: This story contains spoilers from Thursday's episode of Private Practice]

Private Practice's Cooper is a daddy!

Back in his wild days, the doc had a one night stand with Rayanne Erica (My So Called Life's A.J. Langer), who has come to introduce her 8-year-old son Mason to his father. Lest we forget, Cooper (Paul Adelstein) happens to be married to Charlotte (KaDee Strickland), who has never been keen on having children. It's both a nightmare and a dream come true for Cooper!

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"He is somebody who's always wanted children and is with someone who's ambivalent about that," Adelstein tells TVGuide.com. "So, he sees an opportunity to be a father and he's immediately smitten by that idea."

So who's the new lady in Cooper's life? "Erica is a 'pull yourself up by the bootstraps' kind of gal who's comfortable in her own skin though she's in uncomfortable situations," Langer says.

Though Langer is hesitant to compare Erica to her well-known My So Called Life character, she says, "You kind of hope that this is who Rayanne would turn into, something like this where she would go off the rails drastically and eventually get herself on track and pull all the crazy together. Erica is that kind of girl where she probably was a bit wild, but she's really, really bright and very sensitive and capable because she made it through."

Though it's been eight years since Cooper and Erica did the deed, Langer insists Erica didn't keep this a secret for selfish reasons. She's only coming forward now purely for her son's benefit. "Mason is older and has been dreaming of his father for ages and asking questions," Langer says. "A switch flipped, and she was ready and knew it was right."

Of course, the one person this news doesn't sit well with is Charlotte, whose trust issues after last season's attack have only grown with Cooper's recent medical misdeed. "Charlotte is like any other wife would be, she is damn suspicious," Strickland says. "She takes issue with the situation."

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While Cooper is very forthcoming about everything, Charlotte remains cautious, Adelstein says. "She thinks that Erica has ulterior motives and she really wants to protect Cooper. Charlotte goes out of her way to do that, which creates even more of a problem."

With good reason, of course, since there's no telling whether Mason, whom Adelstein likes to call his "mini-Cooper," is actually Cooper's child. "Everybody is going to have doubts and Erica knows that going in," Langer says. 'She's willing to put herself through it because her kid wants to meet his dad."

There will eventually be DNA testing, but Adelstein says that doesn't really matter to Cooper. "Cooper's resistant to that," he says. "He doesn't feel it's necessary. He's adopted, so he doesn't believe that biology necessarily means family. This kid is also, in Cooper's eyes, remarkably similar to him. He loves children and he would never want to shirk from that kind of responsibility."

Of course, showing up after eight years of keeping this secret raises the question of whether Erica has ulterior motives in coming forward. "At this point, I don't think she does," Langer insists. "Everyone has motives and things, and a lot of times, they're not always aware of them, but I feel her intention is pure."

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Her end game may be another story. After so many years alone, Erica may see an opportunity to have a family of her own. "I see her as being a pretty respectful person, but I don't know if she can help it," Langer says. "She's done all this on her own and she probably hasn't many relationships, and he's kind of the perfect guy. All these years of imagining if he's a nightmare or a nice person, and she meets someone who is pretty perfect for her and her son. It opens her mind to all kinds of possibilities."

Whether that means she'll try to rekindle their one-night flame remains to be seen, but Adelstein says, "I have no indication that that's going to happen."

Langer, however, really hopes her character "gets some." She explains, "Everybody seems to on Shonda shows. Maybe her and Charlotte will run off. There was a good [suggestion] online about her perhaps being Amelia's love interest. I'm hoping. We'll see."

Private Practice airs Thursdays at 10/9c on ABC.