While Frozen 2 was another blockbuster success, the filmmakers didn’t exactly know how the movie would play out on screen. Thanks to an iterative process at Disney, the ending was literally made up along the way.

That posed an interesting challenge to songwriting duo Robert Lopez and Kristen Anderson-Lopez, who penned the original films’ iconic “Let it Go.” In some ways, getting the melody (and lyrics) for Frozen 2 was simpler than the original—two of the pair’s songs survived the first screening cuts, compared to zero at the same stage in Frozen. But Frozen set the bar high, and without a clear ending in sight, finishing the film’s final showpiece number (“Show Yourself”) was nearly impossible. Like Elsa, Robert and Kristen went on a similar journey as the lead character, finding this bit of information out at the very end.

Audiences are getting a peek behind the creative curtain in the upcoming Disney+ docuseries Into the Unknown: Making of Frozen 2, which premieres on the SVOD on June 26, and shows the songwriting duo, and fellow writers Jennifer Lee, Chris Buck and Marc Smith, as they tackle the interesting challenge of writing a movie without an end in mind.

“The wonderful thing about working with the same exact people we worked with the first time, is we were all experiencing similar levels of fear and excitement around creating [Frozen 2],” says Kristen. “One of the first things [our colleagues at Disney made clear] is that we were never ever going to be under any pressure to write anything like ‘Let it Go.'”

For the sequel, the film’s crew put together a rough sketch of the movie including scripts, storyboards, voice recordings and of course, songs. Then a “Story Trust” (consisting of the main stakeholders on the movie, as well as every writer and director working on another movie for Disney at the time) came in and gave feedback. The first screening with the Story Trust took place in 2016, and based on the feedback, the the songwriters were left with just two tunes—for everything else they had to go back to the drawing board.

As the married couple worked towards an end number, the songwriters went through seven screenings, with seven endings, before finally landing on the mysterious voice drawing in the main characters (spoiler alert: it’s Elsa’s mom).

That’s not to say every song was a struggle. The duo was able to dust off a previously written piano riff for “Into the Unknown.”

“We wanted something hypnotic because Elsa was being called away by a voice, the voice of where she was meant to be, but in the moment you’re supposed to wonder whether this is something good or something dangerous,” says Robert. They took the riff up an octave, and chipped away at the lyrics until the song came together.

Back-and-forth communication has been key to the duo’s success over their two-decade career.

“Learning how to keep talking [to each other] is so important [because] these art forms are so collaborative, and it can be very challenging to know how to give notes in a way that doesn’t feel like tearing somebody down, or learning chime in without dominating [the conversation],” she says. “It’s something that I continually work towards, and I’m very proud of the way that we have learned to communicate with each other.”

Now in lockdown, with two daughters at home, the pair are faced with even more communication challenges. “We are now the teachers, housekeepers, cooks,” says Kristen. “If our kids are going to be with people, they have to be with us, so we’ve just got a lot fewer hours now to spend in our imagination.”

It’s not like they haven’t created anything, of course. Robert, says that his biggest accomplishment are the recent lockdown-inspired Frozen At Home with Olaf shorts, for which they composed music.

“I’m most proud of because it has the potential to do the most good,” says Robert—which is quite a statement from the EGOT winner. Over the course of his career we wrote the music and lyrics for Broadway musical Avenue Q (earning him a Tony Award), as well as The Book of Mormon (earning him his first Grammy and two Tony Awards). He also worked with Kristen on several children’s series, including Wonder Pets (earning him two Daytime Emmy Awards), before working on Frozen, where the pair won several awards, bringing home the EGOT. He is only the 12th person in history to earn the status, and because he has won two of each award, Robert is also the first person in history to earn double EGOT honor.

Kristen, meanwhile, has written songs for several children’s TV shows such as Wonder Pets on Nick Jr. and Bear in the Big Blue House on Disney Channel. She also wrote and produced the music for the 2011 Disney film Winnie the Pooh before composing the songs for Disney’s Frozen, including “Let it Go,” which won her an Academy Award and two Grammy Awards. She also wrote the songs and lyrics for the 2017 Pixar film Coco, for which she nabbed an Annie and Academy Award.

While in lockdown, they have been able to write four or five songs for their next project, an adaptation of the graphic novel Prince and the Dressmaker by Jen Wang. “When we do write a song now though, it just feels so good to exercise those muscles and forget about where you’re going to get the chicken for tonight’s dinner,” says Kristen.

Undaunted by their close quarters, the pair continue to put out new work, thanks in large part to their established way of working together, says Robert. “It takes communication and truly listening to the other person.”