Rowling is famously private. And crazily famous.

Her Harry Potter novels have sold over 450 million copies since the first was published in 1997, spawning an empire that now encompasses movies, the spinoff “Fantastic Beasts” films, Harry Potter Wizarding World theme parks, and detective novels (written under a pseudonym) that have been made into a television series.

Like much else she touches, her first theatrical venture has been a smash. It earned rave reviews and sold-out houses in London, going on to win in a record-breaking nine categories at last year’s Olivier Awards, the British equivalent of the Tonys.

And yet Rowling, who started out as a struggling single mother, writing her first Harry Potter novel in Edinburgh cafes, seemed — despite an armor of smart wrap dress and high heels — determined to take absolutely nothing for granted.

“We see this as a new challenge,” she said, looking at John Tiffany, the show’s cheerful director, and Jack Thorne, its tall and gangly writer, who were seated with her backstage at the Palace Theater in the West End here. “Broadway is a scary place.”

Broadway is a scary place, with new productions — even those based on beloved titles — routinely failing to live up to their producers’ hopes and dreams. And “Cursed Child” confronts challenges in New York that it didn’t face when it opened here in July 2016 amid more mystery, excitement and anticipation than attends most presidential elections. (And what felt like just about as much media coverage.)

Secrecy about the story line, collectively developed by Rowling, Thorne and Tiffany, fed a growing obsession with what the play would reveal about Harry and Company, and a #keepthesecret campaign encouraged a clublike camaraderie among the preview audiences.

But now that script has been published, reviews have been written and tweets have been tweeted, the plot — a coming-of-age trajectory for Harry’s second son, Albus — is out there. (According to Scholastic, the Potter publisher, the book version of “Cursed Child” has sold over 5 million copies in the United States.)

Unlike most family-oriented Broadway offerings, “Cursed Child” is a play, not a musical, and it will compete in the spring with Disney’s musical adaptation of the animated blockbuster “Frozen.”

“It is unusual to take such a large brand franchise and not musicalize it,” said Sonia Friedman, who, with Colin Callender, has produced the play in London and New York. (It also heads to Melbourne, Australia, next year.) People still occasionally made the mistake, she added: “In every place possible, we say, ‘A new play by ...'”

Although seven original cast members are coming with the show — including Jamie Parker as Harry, Noma Dumezweni as Hermione, Sam Clemmett as Albus, and Anthony Boyle as Scorpius — not one is a marquee name.

One other thing: “Harry Potter and the Cursed Child,” which officially opens on April 22, has a running time of 5 hours 15 minutes, and is staged in two parts (either seen on one day or on different nights).

Will the magic apparate across the ocean? A circus was hurried out the door to help make sure.

‘Something More Reflective’

The play begins where the books end. We are at King’s Cross station as Harry, married to Ginny Weasley and a father of three, sees his middle child, Albus, off to Hogwarts.

The ensuing story encompasses Harry’s difficult relationship with Albus, who develops an intense friendship with Scorpius Malfoy (son of Harry’s school-era enemy, Draco Malfoy), and it suggests that the weight of the past is a continual influence on the present.

It was Friedman and Callender who, six years ago, brought the idea of a play to Rowling, even though she had consistently rebuffed proposals to create stage versions of her novels. “Most of the ideas were about musicals, which I don’t love,” Rowling said, “or redoing the books onstage. I wasn’t interested in doing Harry in every medium.”

Their proposition was different. They suggested extending the story and creating a new work, which intrigued Rowling.

“We talked about loss, fear, bereavement, what it’s like to try to make a family when your own is poor or nonexistent,” she said. “I was really interested in making something more reflective than had been possible in the films. I don’t think we ever deviated from those themes.”

Rowling said that she had been clear that she would commit to the project if she could work with a playwright she felt was right. After Friedman approached Tiffany (a Tony winner for “Once”) to direct, he suggested Thorne, a self-professed Harry Potter nerd with whom he had collaborated on the teenage vampire play “Let the Right One In.”

“When I met John and Jack, I think we knew pretty quickly that the play would center around Albus,” Rowling said, adding that she had always “been interested in Albus Severus. He was the one I thought about. Imagine going to Hogwarts with those two names — which of course I gave him!”

Thorne interjected, “It takes Harry a while to see why those names are a burden, which, from a dramatist’s point of view, is amazing.”

Just as Rowling has meticulously controlled her public appearances, she has also maintained a tight lock on the Potterverse empire.

Her willingness to put her characters in other hands is surprising, but Rowling said she had loved the entire process of co-creating “Cursed Child,” and hadn’t been prepared for the “emotional punch” the play delivered when she saw its final version.

She and her collaborators are also proud to have brought new audiences to the West End. Callender said that market research in the first year of the London production showed that 60 percent of ticket buyers were first-time theatergoers, and that 15 percent had subsequently bought tickets for other shows.

The Magic of Playacting

How to stage a Harry Potter tale without the whiz-bang special effects movies can deploy? Tiffany approached the assignment with one guiding principle.

“The idea that the magic we put onstage could be a version of playacting stories in your bedroom,'’ he explained. “There was something about the aesthetic Jo had created, with cloaks and suitcases, that I wanted to harness directly and simply.”

Thorne predicted that even those loyal fans who’ve digested the best-selling script will be in for a surprise. “The stagecraft is such a massive part of the story that you still don’t know what will happen when you come into the theater,” he said.

Although the play will essentially remain the same on Broadway, the creative team is not taking anything for granted.

“If we see audiences aren’t getting anything, we’ll obviously adjust,” Tiffany said. “We’re always working on the show, and there are certain things about the architecture of the Lyric which means some things will change. It’s a theater with different kinds of possibilities, and I want to exploit them all.”

Rowling laughed. “Never leave a possibility unexploited,” she said.

Callender and Friedman decided on the Lyric after looking at numerous Broadway theaters, all keen to lure the potential Potter gold mine.

“All the theater owners were fantastically generous,” Friedman said. But the British-based Ambassador Theater Group (ATG), which owns the Lyric, she said, “made a proposition which was irresistible to the creative team and to us: They would invest in a space which we could create exactly as we wanted.”

Clearly anticipating an extremely lengthy and profitable run, ATG not only paid for the Lyric’s renovation, but made it financially worthwhile for the Cirque du Soleil show “Paramour,” which had cost $25 million, to move out. (ATG did not respond to questions about the rebuilding cost.) )

An eight-month renovation has resulted in a dramatic conversion of the cavernous theater, once home to the ill-fated musical “Spider-Man: Turn Off the Dark.”

According to Friedman, the first balcony has been brought forward and certain side walls knocked down, “so that it’s narrower and shallower.” This, she said, reduced the seating to 1,500 from around 1,900. (The Palace in London seats 1,300.)

The main entrance has been moved from a clotted 42nd Street to the less crowded, almost discreet, atmosphere of 43rd Street, where elaborate signage has been installed. (Outside the more grandly placed Palace an oversize owl’s nest greeted theatergoers.)

“We learned a lot from the London show about the community feeling that happens when people watch two parts in succession,” she said. “Part of the experience is what happens at the intervals, between the shows.”

Splitting the narrative in two was Callender’s idea, Thorne said. “The stage needs time, breadth,” Tiffany added. “When we thought of the nature of the story and talked about what became the end of Part 1, we just couldn’t get there in an hour.”

Callender said they had realized it was important that viewers kept the same seats for both parts of the play, and recognized their seatmates. (Most people see it in one day, or succeeding nights.) “Then you are on a journey together,” he said.

Callender added that although they could have made the house smaller, they were committed to making 20 percent of the seats available at $40 or less per part.

“Those seats are all over the house, and there isn’t one bad one,” Callender said. “Keeping 1,500 seats is how we could afford to do that.” (Tickets range from $20 to $299 per part, a bit less during previews.)

Asked whether they had encountered any resistance from parents to a costly, 5-hour-plus commitment, Rowling gave a firm no. For kids under 9, she said, “it might be stretching it.”

Friedman pointed out that the majority of the fan base was the generation that had grown up reading Harry Potter, and was now between 25 and 35.

“The fans,” she said, “would like Part 3.”

Exclusion and Acceptance

After years of peace in the Potterverse, “Cursed Child” deals with the forces of darkness and authoritarian power rising — themes that might be read as echoes of the real world, in Europe and the United States.

But Rowling said she did not feel it was a political piece, even as over the years she has come to more full-throatedly espouse her own viewpoints, especially on Twitter. “I’m mouthy,” she said. “I feel like the rest of the world; I’m just venting.”

Yet the themes of exclusion and acceptance that Thorne picked up from the books were important, Tiffany asserted. Rowling nodded emphatically. Voldemort, she said, “was someone who had been excluded and isolated, and we continue to explore that.”

What in Thorne’s writing had surprised her? Rowling pointed to the way he had imagined Scorpius Malfoy.

“He is such a beautiful character, and in many ways the emotional heart of the play,” she said. “And such an amazing foil for Albus, who is tortured and self-involved.”

The last Harry Potter novel came out in 2007, the final film in 2011. At one point, it looked as if that would be that. But with “Cursed Child” and the “Fantastic Beasts” films, the Potterverse lives.

Asked if she ever worried about her fans’ reactions to extending a universe they treasure, Rowling sat up straighter. “I think,” she said calmly, “that it’s up to me what I do with the world I created.”

This article originally appeared in The New York Times.

ROSLYN SULCAS © 2018 The New York Times