“This show absolutely broke me in every way possible,” Holland said at The Crowded Room premiere in New York City Thursday. “I just kept my head down. I dug my heels in, and I just tried my best.”

His fellow EP, Alexandra Milchan, says Holland earned his title as producer. He was involved in the scenes, dialogues, sets and production issues, all while starring in the 10-episode series in which he’s in almost every scene.

The Crowded Room follows Danny Sullivan (Holland), a man who is arrested following his involvement in a shooting in New York City in 1979. Through a series of interviews, with Rya Goodwin (Amanda Seyfried), Danny’s life story begins to unfold, revealing elements of his mysterious past that shaped him.

For the actor, the challenge of playing such a complex character who is “so misunderstood” is what originally drew him to the role. Danny is loosely based on the real-life Billy Milligan, the first person to be acquitted of a major crime due to dissociative identity disorder.

“We definitely are telling a piece of fiction,” Holland explains. “That said, there was a load of research that went into bringing this show to life: reading the book, watching the documentary, watching the film, speaking to experts. It was really important to us to tell this story in an authentic way, as well as a sensitive way.”

The Cherry star says the cast and crew had psychologists on set to keep them in check and ensuring they did the right thing.

Seyfried, who plays a character based on writer and EP Akiva Goldman’s mother, says she appreciates how unapologetic Rya is in The Crowded Room.

“As a professor in the ’70s, men are constantly trying to bury her, get her out of the way, and she just won’t take it,” The Dropout star says. “I always have this hope that I would absorb that confidence when I play characters like this.”

“It was amazing. I love her voice, and I love the way she formulates her questions and how sensitive she is to certain people and how much compassion she has,” Seyfried says. “It’s the most beautiful thing in the world. It was a gift to play her.”

Emmy Rossum, who plays young Danny’s mother Candy, echoes Holland’s sentiment about the roles in the show being taxing.

“I think that the characters in the story asked us to go to incredibly challenging, dark, thrilling places and having scene partners that are equally kind of fearless and unafraid to be vulnerable,” she tells THR. “It’s nice to go to the brink with them and still be holding hands.”

The Crowded Room drops its first three episodes on Apple TV+ June 9, followed by one episode weekly until the finale on July 28.