The producers of Broadway musical “Anastasia” knew they had a big built-in audience for their show. They just didn’t know how big.

As the team behind the production discovered early, the appeal of “Anastasia,” opening April 24 at the Broadhurst Theater and inspired in large part by Fox’s 1997 animated musical, seems to run wide and deep. In its first few weeks on Broadway, the title has proven an unexpectedly strong earner right out of the gate, with weekly grosses coming within spitting distance of $1 million even in abbreviated seven-performance weeks. Last week, when spring-break visitors flooded Times Square, the show jumped by 30% to $1.2 million, suggesting the title already appeals to the tourist crowds that, for most shows, tend to arrive later in the lifespan.

“It’s more than the twentysomething young women who loved the movie as kids,” said Tom Kirdahy, who produces “Anastasia” alongside Stage Entertainment’s Bill Taylor. “We don’t discount their affection for the movie, but there also seems to be something much, much deeper that we’re still exploring and discovering.”

That kind of fanbase brings with it an enhanced sense of responsibility for creators intent on making something that stands alone as a Broadway musical – and that ultimately ended up notably different from the film, with an entirely new antagonist – but one that still satisfies the “Fanastasias” who love the story and the animated film.

“It is a balancing act, trying to acknowledge the fans of the movie, and say we know you’re in the audience and we care about your experience and memories, and at the same time trying to do something that’s stage-viable and interesting,” said director Darko Tresnjak (“A Gentleman’s Guide to Love and Murder”).

Producers and creatives got their first glimpse of their show’s unexpectedly broad fanbase when a teaser trailer for the show hit Facebook in September — and racked up more than 8.5 million views in its first week alone.

“It’s so far beyond what most Broadway shows do,” noted Lisa Cecchini, the VP of media and insights at digital marketer Situation Interactive, which oversees the digital push for “Anastasia.” “Even shows that have brand equity when they’re launching would never get in the reach of the millions organically, with no paid spend behind it.” (The video now stands at 12 million views.)

“Usually you’re happy if you get 50,000 views,” agreed Kirdahy.

A round of market research revealed that those fans weren’t just the young women who saw the film as children. The movie’s reach has extended to an even younger demographic, as the animated featured has endured on VHS, then DVD, then TV and VOD. There’s also a contingent of older-skewing audiences who know the 1956 Ingrid Bergman film, coupled with an even broader group who are fascinated by the true-life mystery of the lost Russian duchess.

All that translates into an unusually broad target demo that can, in terms of marketing, be subdivided and addressed with tailor-made messages. Tickeybuyers are notably younger than they are for most shows — with 50% under the age of 35, according to Cecchini. Marketers and producers have also spotted a high level of international awareness as well.

But it’s the Fanastasias spawned by the animated film that seem most likely to come in with a strong preconceived notion of what the story is and how it should be told. Take, for instance, Christy Altomare, the 30-year-old actress who plays the title character in the show. “The movie was a big deal for me,” she said. “I had the Anya and Dmitri doll. I used to sing ‘Journey to the Past’ in my basement.”

Those fans will recognize a slew of visual nods to the film, as well as the movie’s most familiar tunes — especially “Journey to the Past,” the Oscar-nominated tune that Aaliyah turned into a radio-play hit, and “Once Upon a December.”

But the musical also incorporates almost 20 new numbers by lyricist Lynn Ahrens and composer Stephen Flaherty (“Ragtime,” “Once On This Island”), the duo who also composed the songs for the film. And whereas the movie’s villain was a demonic Rasputin — not to mention his sidekick, the talking albino bat — the musical replaces him with a new antagonist, the Bolshevik general Gleb.

It was the creative team — made up of Ahrens, Flaherty and playwright Terrence McNally (“Ragtime,” “Master Class”) — that, from day one, aimed to differentiate the musical from the movie. McNally, for instance, said he was interested in exploring the real politics of the era, as well as the contrast between the Russian Revolution and the concurrent artistic revolution happening in Paris, where the second act takes place.

None of us wanted to do the animated movie,” Ahrens said. “We wanted to do something that was richer and deeper and more mature.  But then we first started previews in Hartford [where the musical had a tryout run before Broadway], and young women would come in with tiaras and blue dresses and the full costume from the film. And we went, ‘Oh my God, here they are because they love the movie, but we haven’t done the movie!'”

However, the response to the changes from Fanastasias has seemingly been positive, at least so far. According to producer Taylor, it’s the differences that stoke curiosity as much as the similarities to the film. “Those fans are all grown up now, and while they might have an affection for it from the past, you have to create something different if you’re going to sustain that interest,” he said.