Judy Greer admits seeing Renée Zellweger for the first time in full makeup, prosthetics and wardrobe as convicted murderer Pam Hupp while shooting “The Thing About Pam” presented a a unique set of challenges.

“We both looked at each other and started laughing,” Greer, who plays controversial prosecutor Leah Askey in the true-crime series, said Wednesday at the NBCU FYC House in Hollywood during a panel moderated by yours truly. “And then she told me not to make her laugh because her face would fall off.”

Asked if her face ever did “fall off,” Zellweger laughed, “Yes.”

Zellweger revealed the prosthetics did cause her to break out in a rash. “The rash didn’t go away. It was itchy,” she said, laughing.

Even so, she the two-time Oscar winner said, “Are there every too many prosthetics? I don’t think so. What a cool process. I didn’t know anything about that stuff… It was magnificent to sit there and watch it all come together.”

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Josh Duhamel, Judy Greer and Renee Zellweger. Gilbert Flores for Variety

“The Thing About Pam” is based on the podcast of the same name and “Dateline” episodes that chronicled the life of Hupp, who is in prison for murder. She is charged with killing her best friend Betsy Faria and framing her husband Russ Faria as the culprit.

The six-episode show, which premiered on NBC in March, is the first scripted series from NBC News and was produced in collaboration with Blumhouse Television.

“Like everyone who listened to the podcast, I was obsessed,” Zellweger said about taking on the titular role. She’s also a producer on the series. “Driving up and down the 5 — when do you ever wish for more freeway in Los Angeles? It’s like, yes, traffic jam!…I binged it and I was fascinated. A series of escalating absurdities and you’re scratching your head going, ‘How?!’ You’re screaming at the radio, ‘How can that happen?’”

The panel was introduced by “Dateline” host Keith Morrison.

NBC News Studios’ Liz Cole said the expansion of “Dateline” to podcasts inspired the “Pam” adaptation. “We’re looking at a few,” she said of future adaptations. “Pam is the most crazy ass story we’ve told of all the crazy ass stories we’ve told. It really is. That’s why when we were trying to figure out the first one to do, there was nothing really else that we considered.”

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Keith Morrison and Renee Zellweger. Gilbert Flores for Variety