Patti Murin and Colin Donnell are expecting their first child, a daughter, in late July, they tell PEOPLE exclusively

Patti Murin and Colin Donnell have lined up their next roles: parents.

PEOPLE can exclusively reveal that the couple, Chicago Med alums and musical theater stars are expecting their first child together — a baby girl due in the end of July.

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“I’m going to be someone’s mom!” Murin says, almost with disbelief.

“We’re totally thrilled,” Donnell adds. “I don’t think there’s any way to really prepare ourselves. At least twice a day we’re like, ‘Oh my gosh! This is really happening, isn’t it?’ It’s crazy exciting. We’re just super, overwhelmingly happy.”

This will be the first child for Murin, 39, and Donnell, 37. The longtime pet parents, to two 6-year-old rescues, will be married for five years this coming June.

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The timing couldn’t be more perfect for Murin. Just on Sunday, she wrapped her two-year run on Broadway as Princess Anna in the Tony-nominated stage adaptation of the musical Frozen.

“For the past 17½ weeks, I’ve been living this dual life of being two people: a Disney princess and also, pregnant. So I’m really looking forward to closing this chapter and concentrating on preparing for this next adventure,” she says.

“It’s especially great that no one will have to ask, ‘So what are you working on next?’ Because guess what’s next? I’m growing a human!” she jokes. “That’s what I’m really excited about.”

Image zoom Colin Donnell and Patti Murin Dimitrios Kambouris/Getty Images for Entertainment Weekly & People

Having originated the role in Frozen, Murin was with the project for a total of three years, counting workshops and out of town productions.

It was a part she nearly didn’t take. Just before she was cast, Murin learned she was pregnant, and planned to walk away from the musical after already participating in its initial reading and workshop. But a heartbreaking miscarriage at 8 weeks would open her back up to the project.

“That was a really hard choice to make at the time,” Murin recalls. “I was not in the emotional or physical place to do it. I was in the headspace of, ‘Okay, now I know I do want to have a baby and that seems like it should be the plan.’ But Disney called … and Colin and I had to make that decision together — ‘If you’re doing this, you’re not doing that.’ ”

Image zoom Patti Murin in Frozen Deen van Meer

Turns out, doing Frozen would help ready Murin for motherhood in a really unique way. Not only did it remind her about the importance of family, but the relationships she built backstage with the various young actresses playing Anna and Elsa had her wanting a little girl of her own.

“Obviously, no matter what, you want a happy and healthy baby. But all these years in Frozen, it really made me want a girl real bad,” Murin says. “Look, I didn’t even grow up dreaming about being a mom one day. Even getting older, it wasn’t on my radar. But just being around these little actresses, watching them grow up and seeing how mature they’ve become, it was like great practice and it woke something up inside of me.”

Adds the mom-to-be, “I love them to pieces. I feel ready to raise a girl because I’m in a place as a woman where I feel like I know something about how I want them to turn out. It’s made me excited to have a little spitfire of a daughter of my own.”

Murin learned she was pregnant in November while she and O’Donnell were in Iceland, filming their Hallmark original movie, Love in Iceland.

The news took both of them by surprise. “We had sort of talked about trying again, but figured we’d decide after I finished Frozen. We were going to do that ‘not NOT trying’ thing where you just throw caution into the wind. And then, it just happened,” she says. “We are just literally a lesson for everyone out there that this is what happens when two adults don’t use protection. I don’t think either of us realized it would happen quite so quickly, but we’re very fortunate it did.”

“We’re right at that age where a bunch of our friends have kids,” Donnell says, explaining this will be his parents’ fifth grandchild and Murin’s parents’ sixth. “My brothers and most of Patti’s brothers and sisters have kids, so we’re constantly surrounded by nieces and nephews. The timing couldn’t have worked out better, I think.”

“Plus, that’s the thing about this business: you kind of take what you get when you get it,” Murin jokes. “You can’t be super picky in the beginning and there’s just never time to plan. So I’m glad it worked out that way.”

But just because the timing worked out, doesn’t mean all was easy. Because she experienced a miscarriage previously at the 8-week mark, Murin says those first two months were especially hard for her and Donnell.

“We were excited, but we were also very nervous,” she remembers. “We knew I had a miscarriage before. We knew I have a slightly heart-shaped uterus, which makes it harder for pregnancies to implant. But we didn’t know if the miscarriage the first time around was a fluke or if it was really because of a reason and it was going to happen again. So we kind of talked about it but we didn’t make plans. There was a caution there.”

That went away as soon as the pair saw that heartbeat during that 8 week ultrasound. “We cried,” Murin says. “It was a complete relief. Like, all that fear just evaporated. Of course, you still hold your breath a bit. You leave a doctor’s appointment and you’re relieved and then the paranoia builds until the next one. But none, for me, was as hard as that first one.”

Image zoom Patti Murin and Colin Donnell Walter McBride/Getty

Image zoom Patti Murin and Colin Donnel with their dogs, Milo and Petey Courtesy Patti Murin

Since then, Murin and Donnell have just been counting down the days and picking out baby names (“We have names picked out but we’re not going to tell anyone until she’s here,” Murin says).

They’re also taking in advice when they can get it, especially from their close friends in the Broadway family.

“There’s so much support out there. Every time we’ve gotten to tell someone, they’ve just been so positive,” Donnell says. “It’s really sweet and one of the coolest things about having a kid in what we do is that there is such a tight-knit community. You can’t beat it.”

“This is going to be the most loved baby girl in the world from all the support we’ve gotten,” Murin says.

Ultimately, both are just looking forward for the next step. They just need a vacation first.

“Right now the two of us are going to be in-between things, so we’re lucky to have time together,” says Donnell, who was recently cast in the Broadway-bound stage adaptation of Almost Famous. “Patti’s just been amazing. Literally, I cannot believe she did Frozen while going through the first and part of the second trimester of her pregnancy. That’s some superhuman stuff there. So now that she’s done, we’re going to travel someplace tropical so she can catch up on her rest and we can just relax.”