There are a few moments that change a person, really and truly change them, making it impossible for them to ever be the person they were before The Incident again. The same is true for shows, the best of which grow and evolve right alongside its lead characters. Crazy Ex-Girflriend's second season finale featured one of those moments: with Rebecca Bunch (Rachel Bloom) being left at the altar by her long-time obsession/camp boyfriend Josh Chan (Vincent Rodriguez III).

When the Golden Globe-winning CW series returns, it will no longer be the darkly funny rom-com focused on Josh and Rebecca's will-they-won't-they relationship, but draw inspirations from the well of iconic stalker thrillers like Fatal Attraction and Swimfan -- all without losing its sharp, satirical sense of humor and high-concept, often absurdist, musical numbers.

If that sounds like a tall order, it is. And yet Crazy Ex-Girlfriend's third season makes it look easy. Season 3 is poised to be a landmark moment for the series, as it closes chapters that have defined the show since the beginning and pushes the narrative forward into exciting new territory. In addition to exploring the fallout of the end of her relationship with Josh, the series will also dig deeper into Rebecca's mental health and even give her an official diagnosis, which will send Rebecca down a whole new path of self-identification and -discovery.

Crazy Ex-Girlfriend Will Officially Diagnose Rebecca This Season

For more of what to expect of Crazy Ex-Girlfriend's third season, including the chances of Greg (Santino Fontana) returning, we spoke with showrunner Aline Brosh McKenna.

Rachel previously said that the first two seasons were a rom-com for Rebecca and now it's going to be more of a stalker thriller.
Aline Brosh McKenna:
You know, I think the thing you think when you hear the title Crazy Ex-Girlfriend, which is a comedic look at a Fatal Attraction-type character, this is really the season where we move into that space. I don't know that the tone — the tone is more intense, but it's still a comedy. It's darker in certain ways. I think it's emotionally more intense and more specific and a little less light and airy than it was in the first season, for sure, but that's the progression of the story.

Josh has such a habit of jumping into things without thinking.
McKenna:
Yes. Relationships, priesthood, jobs. He's not really a look-before-you-leap kind of guy, combined with him being a bit cowardly, so he's got a lot to learn. It's a really great season for him because there's been this rupture with her and so even though they're not engaged anymore, he has to figure out what his life is about because of her. His life is blown up a bit, so he needs to figure out what his values are and what he's going to do.

I feel like so many characters have grown so much over the course of the series, but Josh has been very stagnant.
McKenna:
Yes, because he's somebody, if she had not shown up, he would have stayed the way he always was. I always think it's interesting that if it were not for that chance meeting on the street in New York, his life would have been probably pretty ordinary. He would have married Valencia, had kids and her life would have been different, his life would have been different. And I think one of the things we love about it is that chance meeting of exes on the street changes not just their entire lives, but of all the people around them.

Crazy Ex-Girlfriend: Will Greg Return in Season 3?

Paula (Donna Lynne Champlin) has always been Rebecca's biggest supporter and Rebecca and Josh's biggest supporter. How will she respond to the breakup?
McKenna:
She will remain Rebecca's biggest supporter. The core of the show is that love story between these two women and the connection between the two women. I don't think it's an accident that the show's being written by two women who are 20 years apart in age, so that to us is the core. And one thing is whenever we find ourselves at a pause in the storytelling or we get blocked in the storytelling, we always go back to Paula, because Paula is, in many ways, an expression of another side of Rebecca. But they're really soulmates in many ways.

I think everyone has really been that friend where after a bad breakup you're like, "OK, well now I hate this guy too." How much is she going to commit to that role?
McKenna:
It's a fine line because one of the things Paula already knows is that she has a tendency to be an enabler, so it's something that she faces in herself. So balancing her desire to help Rebecca in a healthy way with her tendency to enable her kind of hatred of certain aspects of male behavior, it's not simple. Its not a simple equation for Paula.

Paula just had an amazing season and she really has come so far since the pilot. What are her next steps?
McKenna: I mean, there are so many. I think one of the things we didn't explore as much last year is where Paula comes from in her past and family. We explore Paula's family and get to see them more. And as she learns the lessons that she's learning from interacting with Rebecca, she takes those — you know, she never would have tried to become a lawyer without her, but there are sacrifices and choices that she's made for that friendship that have, again, repercussions in her marriage and family life. And we're going to do an episode where we go home and see her family.

I loved the girl group stuff last season. Why do you think it is so important to feature this girl group and show these women who many would assume — like Valencia (Gabrielle Ruiz) and Rebecca — wouldn't be friends?
McKenna: It kind of happened organically. It wasn't something we set out to do, really. But one thing I love about that girl group is that none of them have really had friends before. Rebecca has not had good luck with her friendships, Paula's not really very open to friendships with women, generally. I think Paula was a very lonely person. Heather is so dry and Valencia we know just really doesn't get along well with women. We started to love the idea of women who have not had a lot of success in their relationships with other women sort of forming this friendship without really quite knowing how to do it.

How will Heather (Vella Lovell) and Valencia react to the Rebecca the Scorned Woman attitude?
McKenna:
We see them in the end of the season finale, they're on board. The question is how on board will they be for how long and how much do they know about what's going on.

I'm so happy Scott Michael Foster is going to be a series regular. There's such a great spark between Nathaniel and Rebecca.
McKenna:
There really is. I'll tell you a secret about him, which is that he's the best. He's the nicest guy, he's so friendly, he's so warm. He's great with Rachel. One of the things about, for Rachel, scene partners, is you need people who really protect you and make you feel safe, and Vinnie has obviously always done that. Vinnie and Rachel have a very close relationship. He always takes care of her in that respect, and Scott is just like that too. He's very kind and very protective when they do love scenes. We're so lucky we found them.

Crazy Ex-Girlfriend: Rebecca Is Out For Revenge in the First Season 3 Teaser

How does that relationship develop over the course of the season?
McKenna:
I think we've seen that they have an undeniable attraction there. So it's sort of a question of what form that takes.

I love everyone, but Daryl (Pete Gardner) and White Josh (David Hull) are my favorites. What is next for them? They've had some ups and downs recently.
McKenna:
They're going to continue to have ups and downs. Sometimes the supporting characters, once they're in a romance, they get put off to the side, so we're pretty determined not to do that. You know, they're two very different people from very different backgrounds, different life experiences, trying to have a relationship. So they have their issues and problems just like any couple.

As a Greg fan I have to ask, school has breaks, so is there any chance we'll see him this season?
McKenna:
As Rachel said, his impact on her life doesn't go away. And if we were bringing him back, it wouldn't be fun if we told. But also, I would say we're open to it if the story is there. The story is the most important thing. We completed his arc in many ways, so all I will say is that there will be things pertaining to Greg and we're open to having Greg come back at some point when it's relevant to the story.

Crazy Ex-Girlfriend returns for Season 3 on Friday, Oct. 13 at 8/7c on the CW.

(Full disclosure: TV Guide is owned by CBS, one of the CW's parent companies.)