Frozen's massive popularity with its record- breaking US$1.2-billion (S$1.7-billion) worldwide box office makes one question obvious: When is the sequel coming?

Chris Buck, who directed the movie with Jennifer Lee, flatly denies that work has started on the follow-up. Released in 2013, the adaptation of the Snow Queen fairy tale has since become the highest-grossing animated movie of all time, thanks in no small measure to the earworm Let It Go.

"It's swirling out there," is all Buck, 54, will be drawn into saying about plans for a second feature.

Not that Disney can be accused of leaving money on the table.

Much to the consternation of parents everywhere, Frozen has become a mini-industry in itself. Its characters - the princesses Anna and Elsa, Olaf the snowman, Kristoff the ice merchant and his companion, the reindeer Sven - appear in theme park rides, an ice-skating show and, of course, toys, apparel and collectibles. There is a Frozen-themed tour of Norway, the country on which the landscapes in the movie were based.

Directors Lee and Buck and producer Peter Del Vecho have in the meantime made Frozen Fever, a short that will be screened as a package with the live-action film Cinderella, which opens in Singapore tomorrow.

In the seven-minute mini-movie, Elsa (Idina Menzel) catches a cold while she organises Anna's birthday. Havoc ensues when her sneezes cause dozens of tiny, hyperactive snow creatures - dubbed "Snowgies" by Disney - to appear.

Creating a new story for Elsa and Anna could give anyone sleepless nights. Get it wrong and you will earn the ire of its fiercely loyal audience, such as when Pixar's Monsters University (2013), the sequel to the much-loved Monsters Inc (2001), was judged by many to be inferior to the original.

Buck calls the experience of returning to the magical land of Elsa and Anna's Arendelle "a mixed bag".

Work on the short film began soon after the end of Frozen's cinema run, leaving little time for its creators to put distance between them and the work. "Frozen is a round-the-world phenomenon and it hasn't really ended. We are still doing quite a few projects," says Buck, referring to the various franchise spin-offs.

Lee, for example, is involved in the Broadway adaptation of the film, which won an Oscar for Best Animated Feature and Best Original Song for Let It Go.

Buck adds: "That was our hesitation - would we be tired of the Frozen world? But once you get into that world, you say, 'Gosh, I love these characters.'"

Producer Del Vecho thinks fans will be happy with how the short includes a key component of the Frozen DNA. "Music was such a big part of it, so we knew there had to be a song," he says.

The tune, Making Today A Perfect Day, like Let It Go, was written by the husband-and-wife team of Robert Lopez and Kristen Anderson-Lopez.

Lee and Menzel have made tongue-in-cheek apologies to parents of children obsessed with the song. Del Vecho is also aware of the parental pain the song has triggered. "We know many kids sing the song day after day after day. Some of them I know personally," he says.

One solution, he says, might be for a new Frozen song to come take its place. Frozen Fever has it covered, he says, laughing.

The Frozen phenomenon is all the more remarkable because of how far the story strays from Disney princess plots and classic fairy tales. The relationship at its heart is the family bond between sisters, rather than a romantic one between a male and female character.

Also, true love's kiss takes on a new meaning, while love at first sight is not such a good idea.

The story is aware of classic fairy tale set-ups, if only to use them to illustrate how different things are today, says Buck. "Society has changed. Anna wants to marry Hans the first time she meets him and everyone starts poking fun at the idea. Anna wants to do it and yet we show that maybe you shouldn't marry the first man you meet," he says.

He and screenwriter Lee hammered out the characters of Elsa and Anna, discussing questions such as, "Is Elsa becoming too much like a superhero and losing her humanity?"

"We didn't want them to become guys in dresses," he says.

Frozen Fever will be screened as a package with Cinderella, which opens in Singapore tomorrow.