The actress broke down her character's shocking health revelation from the Part 1 finale of the Netflix series.
Spoiler alert! Do not proceed if you have not watched Part 1 of Netflix's final season of Firefly Lane.
Netflix's Firefly Lane leaned into the tears and heartbreak in Part 1 of its second and final season -- and set up a devastating health predicament for one of the women. While the first nine episodes answered a lot of lingering questions about what tore Kate and Tully's friendship apart and offered up several intriguing romantic updates, it also introduced new challenges and obstacles for the former BFFs to face apart -- for now.
In one of the most heartbreaking reveals in Part 1 of the hour-long drama, Sarah Chalke's Kate -- after recently getting re-engaged to Johnny (Ben Lawson) -- notices a severe rash that's formed on one of her breasts. When she gets it checked out by a doctor, Kate receives the devastating news that that rash is not just easily remedied by medication. It in fact is a rare and aggressive form of Stage 3 breast cancer. Alone in the doctor's office as she receives the news, her friendship with Tully still not repaired after she learned Tully was drunk behind the wheel after picking Marah up at a frat party when they got into their accident, Kate's world has just been turned upside down.
As she tries to digest this life-changing news, Kate finds herself at Tully's apartment building, deciding that she needed her best friend more than ever and putting away their differences for the time being. However, in a cruel act of fate, Kate misses her estranged best friend by seconds as she enters one elevator to go up to the penthouse, arriving just a sliver too late as Tully walks into the other elevator to go down to embark on her months-long trip in Antarctica. Realizing that Tully was not going to answer the door as she tearfully pounds on the door, Kate crumbles to the ground as she cries.
"It was really emotional and I obviously had read the book, so you knew that eventually that would be coming up," Chalke told ET's Deidre Behar of Kate's cancer diagnosis, referring to the Kristin Hannah novel the series is based on. "I just loved how [showrunner] Maggie [Friedman] wrote it, but it was really emotional because obviously there’s nobody whose lives had not been touched by cancer."
"We lost my aunt and my grandmother to cancer. There were crew members who came up to me and told me their stories, so when you're shooting and you become very close with this crew when you’re looking into the eyes of those people as you’re doing that scene, yeah it was definitely... a lot of heavy days there that last few weeks of filming," the actress added.
Chalke shared that filming those specific scenes was particularly difficult, adding that she often would shake off the heaviness by going home and being with her two kids.
"One of the huge gifts about this job too was that there’s always that balance. One minute you're dancing to an '80s song and then the next day you’re doing something like that, so I feel like we also wanted that experience for the viewer too," Chalke said. "So you get a bit of everything so that it gets heavy, but you also get the light side of it too."
Asked whether Kate will come out of her cancer battle a survivor, Chalke danced around the question, hinting that that will play out in Part 2, which drops some time in 2023. (In Hannah's book, Kate dies from cancer.)
"Oh, I can't answer that," she teased, adding that they've "shot all of" the final season. "I know all of the things, but that is something that plays out through the last half of the season."
Chalke acknowledged that Kate's health battle shapes her character's arc in the last seven episodes of the series quite significantly. "It really does," she emphasized. "I think, again, it's such a fine [line] just threading the needle of how to tell the story, have the balance of what's happening in the '70s, the '80s. They go into the '90s a bunch and then obviously in the aughts. That's all I can say 'cause I don't want to give it away."
The actress again played coy when asked if Tully eventually learns of Kate's diagnosis and lends an olive branch of support.
"I am under very big lock and key not to reveal anything about the back half, so I can't say anything," Chalke skirted, adding later she's optimistic Tully and Kate will find their way back to each other through this crucial time: "That's how walk through life is remaining hopeful, so when I read the scripts, every time one would into my box, I'd be like, 'What's gonna happen?,' 'cause obviously there's the huge cliffhanger at the end of season 1. But then there's mini cliffhangers that happen sort of throughout the season so you're constantly going [gasps]."
Chalke expressed the heartbreak knowing that Kate missed Tully by mere seconds in the elevator, but her decision to go to her estranged friend -- even amid uncertainty surrounding their friendship -- was a statement in itself. Even though it didn't turn out the way Kate hoped.
"I feel like what I loved about that in the end of the season was, as much as has come between them, when you know s**t really hits the fan she just needs Tully," she said of that midseason finale-ending scene. "Obviously everything else melts away and she goes to her and then [Tully's] not there."
"It’s a matter of moments!" Chalke said.
With the final episodes of the series looming, Chalke said she's most excited for fans of Firefly Lane to find out what happens to Tully and Kate's romantic futures -- Tully potentially with Danny, Kate with Johnny -- as well as Kate's health journey.
"I want everyone to sort of get to see what happens there," the actress elaborated. "And also just to see the through line of Kate and Johnny and what happens with them."
As for how she'd describe Part 2, if the first half was emotional, keep those tissue boxes close by. "Oh very [emotional]," Chalke promised. "I think it's 10. It's funny and it's painful and moving. I was quite moved when I read [the final episodes]."
Part 1 of Firefly Lane's final season is streaming now on Netflix.