Mark Ruffalo’s Surprise Baby News Rocks Siblings Lili Reinhart, Cooper Raiff (Exclusive)

Cooper Raiff and Lili Reinhart play codependent siblings grappling with all the scary changes of adulthood in Hal & Harper.

PEOPLE can exclusively premiere the trailer for the series, which premiered at Sundance 2025, and stars Raiff, 28, and Reinhart, 29, as the eponymous siblings, with Mark Ruffalo as their dad.

The trailer begins with a taste of just how tight siblings Hal (Raiff) and Harper (Reinhart) are, as Hal calls his sister in the middle of the night, asking her to get “dessert and fries with me” at 3 a.m.

“McDonald’s is so far away,” Harper laments, and Hal quips in response, “Yeah, you’re right, and traffic is pretty terrible right now.”

“Okay, idiot, where do I pick you up?” she asks, and Hal lifts up her bedroom window and somersaults into her room as he says, “You don’t. Because I’m already here.”

Ruffalo, 57, drops some big news in the trailer: he’s having a baby with his girlfriend Kate (Betty Gilpin). It’s a revelation that surprises both Hal and Harper — and Christopher Meyer quips that it’s “not possible” that Hal’s dad is having a baby — but Hal seems to be taking it particularly hard.

“I’m really upset about our childhood house being sold,” he confesses to Harper. “I’m so okay with him having a baby, but I just don’t want him to sell our childhood house.”

While their dad admits that they both “had to grow up way too fast,” the siblings are navigating their changing relationship.

Hal asks Harper, “Are we friends?” and she says, “We’re brother and sister.” Then, she gives in: “I guess we can be friends too.”

During an emotional moment, Harper breaks down to Addison Timlin, who tells her, “You are safe. All of the feelings are safe.”

As the trailer ends, their dad makes a powerful statement, as he says, “There’s more to life than family.”

The eight-episode series, which was created and directed by Raiff, also stars Alyah Chanelle Scott and Havana Rose Liu.

Per the official description, Hal and Harper’s “closeness is both their comfort and their curse” and when ” their father announces he’s having a baby with his girlfriend, Kate, it forces the siblings to reexamine their past and reckon with the versions of themselves they’ve carried into adulthood.”

“As the lines blur between closeness and codependence, memory and reality, Hal & Harper explores how a bond formed in childhood can shape every relationship that comes after — for better or worse.”

In an Instagram post following the Sundance premiere, Reinhart called her role in the series the “greatest honor of my career,” as she said, “Our hearts are on our sleeves with this show and I’m more than grateful that this story is touching audiences so deeply. We need vulnerability, grief, healing & love on our screens now more than ever.”

Raiff also posted after the festival, as he wrote in a post, “I wish I could tell you how much this show means to me but I think you’ll understand. Thanks to everyone who made it happen. I love you.”

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The first two episodes of Hal & Harper premiere Oct. 19 on MUBI, followed by weekly releases through Nov. 30.