Mandy Patinkin's Family Secrets Inspired Him to Take on Bombshell “Brilliant Minds” Role: 'It Made Lying a Cancer to Me' (Exclusive)

Warning: this story contains spoilers from the Jan. 6 season finale of Brilliant Minds.

When Mandy Patinkin stepped into rehearsals for his guest role on NBC's medical drama Brilliant Minds, he also stepped back in time, into his own family's history.

The Michael Grassi-led procedural is loosely based on the real life of Oliver Sacks, a neurologist who was one of the first to investigate mental health. Just like the show's main character, Dr. Oliver Wolf (Zachary Quinto), Sacks was motivated to pursue a career in this field because a close family member struggled with a mental illness, and it was treated as a big secret.

"Oliver Sacks then dedicated his life to writing about these things and talking about them and listening: all of these things that are so important to Brilliant Minds," Grassi tells PEOPLE. "We're sort of trying to carry that torch forward."

The show follows Dr. Wolf, who takes on a new neurology case each episode, alongside his interns Van (Alex MacNicoll), Ericka (Ashleigh LaThrop), Jacob (Spence Moore II) and Dana (Aury Krebs). The doctor, who has prosopagnosia, or facial blindness, also starts up a romance with neurosurgeon Dr. Josh Nichols (Teddy Sears) and contends with the death of his father, who struggled with mental illness throughout his life.

In the final two episodes of Brilliant Minds' first season, Patinkin guest stars in a bombshell role. After helping Dr. Wolf and Dr. Nichols during a terrifying building collapse, he reveals himself to be Wolf's father, alive and well, over 20 years after his son believed he had died.

Patinkin tells PEOPLE that he got a call from Grassi about the role while sitting in a chair that he "inherited" from his time on Homeland. After quickly requesting to put him on speaker so Patinkin's longtime wife, Kathryn Grody, could hear — "because she's my boss," the actor says — Grassi got to work explaining the show's concept and the pivotal role of Wolf's dad.

"My wife kept looking at me and her eyebrows kept going up. She was saying, 'You should pay attention. You have interesting relationships with your sons. You might find this interesting,' " Patinkin recalls of that first conversation, referencing their sons Isaac and Gideon.

Related: Who Is Mandy Patinkin's Wife? All About Kathryn Grody

He then got the pilot from Grassi, as the final episodes hadn't been written yet, and remembers thinking it was so "beautiful" for a first episode. The pilot also touched Patinkin because it featured a moving performance by André De Shields who The Princess Bride actor had seen in a play in his teens, just as he was being bit by the acting bug.

For Grassi's part, he couldn't imagine another actor in the role. "I would say Mandy was the only person we imagined and talked about in the writer's room originally pitching the series," he says. "When I pitched Zachary what his season story would be, I said, 'At the end of the season, dad arrives, and imagine it's Mandy Patinkin.' "

Before digging too deeply into the character, who ultimately causes Wolf to question all of his relationships after he realizes he has been lied to for years, Patinkin says he wanted the relationship to be "hopeful."

"I want it to be filled with life and love and kindness. I don't want to dredge up landfills that are poisoning the earth of their souls," he remembers saying to Grassi.

Quickly though, as Patinkin's own history caught up to him, this dream felt unattainable. "I thought I could do that but I couldn't. I would constantly find myself breaking down because of things you can't help but think about as a parent: 'Did I screw up? Did I hurt my kid this way? Did I hurt my wife? Is it recoverable?' " Patinkin recalls.

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As they got deeper into rehearsals and filming, the scenes where Wolf's parents' lies come out "hit a nerve" for Patinkin, bringing up two family secrets and deep emotions that he couldn't ignore.

One memory that kept tugging at him was a big reveal he received on Henry Louis Gates Jr.'s Finding Your Roots in 2021. At the urging of his son Gideon, Patinkin went on the show and learned of a big family secret that changed the way he viewed his ancestry.

"My generation was told that we didn't lose anybody in the Holocaust but the show revealed that there were many, and they gave me the names," he says. "They did all of this on camera for five and a half hours, and I lost it repeatedly."

Patinkin remembers feeling completely blindsided by the bombshell and thinking of his family members, "How could you not have shared this with us?"

Related: Mandy Patinkin Cries as He Tells a Fan the Emotional Story Behind His Iconic 'Princess Bride' Line

Much like in Brilliant Minds, Patinkin thinks these secret keepers felt they were doing the right thing. He adds of his own family experience, "They did it for a lot of reasons: to protect us, to deny it for themselves, on and on and on."

Getting into character for the medical procedural also brought up Patinkin's own memories of his ailing father, who received a cancer diagnosis but was told by everyone, including his doctor, that it was actually hepatitis. Many feared he couldn't take the news and everyone played along with the lie.

"My dad was no idiot. It didn't take him more than five minutes to figure out that this ain't hepatitis," Patinkin says. "I lied with everyone else. And you don't ever get that time back to be with your father in any way you might imagine. It made lying a cancer to me, worse than any cancer that exists."

Grassi agrees and says that a major part of bringing Brilliant Minds to the screen was about truth-telling and "being in conversation with each other and listening to each other."

In the end, it seems like Patinkin's wife, Grody, was on to something, and the guest-starring role really did end up being an "interesting journey" that was "beneficial" to the actor's work and personal healing.

In the end, Grassi was bowled over by Patinkin's dedication to the story and his performance.

"I have worked in this business for some time now, and your dreams don't always come true. Sometimes they do come true, though, and you get to work with someone like Mandy," he says. "It makes me wanna say, do meet your heroes because this has been an incredible experience."

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Brilliant Minds can be streamed on Peacock.

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