Fifth Harmony has already defied the odds -- by selling nearly half-a-million albums in a career launched on TV's The X Factor less than five years ago, by scoring two top five Billboard Hot 100 hits ("Worth It” in 2015 and "Work from Home” earlier this year) and by proving that the group, constructed on the whim and A&R savvy of Simon Cowell and developed with the seasoned industry know-how of Epic Records chairman L.A. Reid, has a purpose in the pop world. So how did things turn so sour?

In what's been a volley of she said/they said statements over the last 72 hours, following the girl group's routine performance at their final Jingle Ball stop in Miami on Dec. 18, Fifth Harmony members Ally Brooke, 23, Normani Kordei, 20, Dinah Jane, 19, and Lauren Jauregui, 20, announced via social media that Camila Cabello had, in their words, "decided to leave” the group. The unexpected statement was followed by Cabello's own response that, "Saying that I was 'leaving the group' is simply not true,” Harmonizers, as their fans are known, have taken to social media to express their confusion over what really led to the act's downsizing from five to four. At the same time, many in the industry are wondering what happens to the hashtag-christened "Fourth Harmony” from here -- especially considering the label is staring down a deadline at the end of December by which the company has to decide whether to pick up the group's option for a third full-length album (Epic Records has not commented on the status of the deal; reps for Fifth Harmony and Cabello declined further comment).

Although Fifth Harmony's recording contracts are structured as individual solo deals, allowing them to make music both as a unit and on their own, according to multiple sources, tensions had been festering among the group members for some time as Cabello increasingly voiced her desire to pursue a career outside the group. Cabello's aspirations were no surprise to her bandmates: Over 18 months, she'd been open about solo prospects in the press. She had also enlisted her own manager, Roger Gold, independent of Fifth Harmony's representative -- Jared Paul (New Kids on the Block) in the post-X Factor years, until Dec. 2015 when Larry Rudolph of Maverick (Britney Spears) took over for the group. But once Cabello's hit duet with Shawn Mendes, "I Know What You Did Last Summer,” was released in November 2015, talks began in earnest concerning the future of the group as a five-piece and rumors began to spread that Fifth Harmony was unraveling.

But while a source close to the situation insists "Camila could not have been clearer about her desire to leave the group,” refusing repeated outreach and suggestions of meetings and group discussions, here is where the details get fuzzy -- who wasn't speaking to whom, for one. Was it Cabello versus the four, with an occasional ally in Dinah Jane? Or was it a full-on silent treatment, paused only when a group appearance on stage or in the media demanded it? And was Cabello replaceable (an idea to launch a search for a new singer via a reality show was discussed and shot down) or is it wiser for Fifth Harmony as a brand to move forward with four? After all, members Lauren Jauregui and Normani Kordei had also announced projects outside the group, and had been asserting more independence of late -- Jauregui's recent collaboration with Marian Hill and coming out as bisexual, for instance.

The idea of a "hiatus” was offered by the Cabello camp, but the other members of Fifth Harmony would not agree to waiting out her solo career. The iron was hot now.

There were multiple attempts at interventions -- from bringing a therapist out on the road "to help the girls sort out their issues,” says an insider, who claims that all but Cabello participated in sessions with the licensed psychologist, to scheduling a "come to Jesus” sit-down with Reid, management and the girls for which Cabello was purportedly a no-show. But a source close to Cabello contends that a group meeting with Reid was "never confirmed” and that previous sit-downs with a therapist would "historically devolve into a four-against-one scenario, much like the dynamic in the current public battle of statements we are seeing, and were largely unproductive.” Instead, "Camila felt that the best way to communicate effectively with her bandmates was one-on-one, which she did during the European tour.”

Even Simon Cowell, whose Syco label is a Sony Music imprint (as is Epic), got involved, advising the group members to look to the bigger picture: that there's value in keeping this massive machine -- 7 million U.S. digital downloads sold and 1.6 billion U.S. on-demand streams, as of Dec. 15, according to Nielsen Music -- going as long as possible. "The girls wanted the group to stay together for the business,” adds a source familiar with the circumstances. But even Cowell eventually relented to the idea of Cabello's exit, having been down the road before with One Direction, among many other acts. "[Cowell] was the voice of reason. He would say, 'You can't make people work together.'”

Others on the periphery point out that a solo album by Cabello and another release by Fifth Harmony were not mutually exclusive. But again, a Cabello source paints a different picture. "The group's management made it clear that if she wanted to make any more solo music, it wouldn't work for them,” says the insider.

Being in a girl group "is not for the faint of heart,” offers veteran producer Ron Fair, who has worked with such artists as Christina Aguilera and Pussycat Dolls. "The business is so hard and unforgiving that only a rarefied few make it to hits and awards shows and fulfillment of their dreams.” Fair stresses that the ambitions of girl group members are often rooted in early childhood and through the years become "like a belief system.” Once the group dynamic comes into play, however, "and as there is more and more success, it turns into, 'What about me?' We've seen it fictionalized in Dreamgirls and in the real-life story of The Supremes. Very few girl groups have been able to stay together for a protracted period of time.”

One thing that isn't being debated, however, is Cabello's potential as a breakout star. While it's not unusual for one member of a group to try his or her hand at a solo career -- even while still attached to the group, as Beyoncé did while still in Destiny's Child -- it is rather uncommon for someone to stand out in a collective as much as Cabello has over the past years. In terms of collaborations, her top 20 hit with Mendes highlighted Cabello's breathy delivery, while her authoritative turn on Machine Gun Kelly's "Bad Things” launched the fledgling rapper into the Hot 100 top 10. Yet Cabello has also demonstrated -- through her hilariously self-deprecating Snapchat antics, revealing interview quotes and intimate interactions with her 3.2 million Twitter followers -- a superstar's knack for connecting with fans and standing out from her surroundings.

Recalling the night during which Mendes, Cabello and songwriter Ido Zmishlany came up with the song "I Know What You Did Last Summer” in a backstage dressing room following Mendes' opening slot on the Taylor Swift 1989 tour, Island Records president and CEO David Massey describes Cabello as being "completely involved in the process.” It was clear to him, he tells Billboard, that "she was a real talent and brought this incredibly energy and enthusiasm” to the track.

In fact, Fifth Harmony's label, Epic Records, has been planning a Cabello solo album for the better part of a year, putting the 19-year-old in the studio with such hitmakers as Benny Blanco and Diplo in addition to songwriters Madison Love ("Bad Things”), Johnny Mitchell and Amarr, and producers Futuristics ("Bad Things”) and Serm (Sean Paul's "No Lie”). According to a source, the album is well on its way, with sessions booked through January. Cabello's first solo single could be out as soon as March or April with an album to follow in the summer.

But right now, five girls and their various representatives (three of the five have their own attorneys and lawyer Dina LaPolt represents the group) are dealing with a very cold December. Between the 18th of the month (a day the four girls understood to be Cabello's last with the group, while a source in the Cabello camp claims it only marked the end of their commitments on this album cycle and "did not mean that she wanted to withdraw from the band”) and the end of the year, when Epic's option for a third album by Fifth Harmony comes up, Harmonizers' entire universe could be upended.

"I think it's a huge mistake,” says one industry power player who believes they should have stuck it out for a third album. "This is the group's moment. They just had the biggest record of their career and the next record is 'the one.' [Camila has] had success but all with singles that aren't hers.” (Worth noting: Cabello and Machine Gun Kelly share equal billing on "Bad Things.")

Fifth Harmony has sold 424,000 albums in the U.S. to date, but its debut full-length set, Reflection, moved twice as many units as their most recent album, 7/27, so the metrics don't exactly point to a sure thing either. From the label's perspective, even on the heels of three top 40 hits, to put out a new Fifth Harmony album is an expensive endeavor and a risky one. The safer bet for Epic might be to throw its weight behind Cabello as tomorrow's star. (Also worth noting: On the same week when their internal drama went public, Fifth Harmony's latest single, "That's My Girl,” dropped out of the Hot 100 and its spins at top 40 radio were cut in half, signaling that the plug may have been pulled on further promotion of the song.)

If there's a backlash beyond the fan army turf war, it may be due to the way the announcements were handled. Unlike One Direction, another X Factor-spawned group, where exiting member Zayn Malik released a statement at the same time as his former bandmates and Cowell ("I have to do what feels right in my heart,” Malik's read, followed by praise for the group that put him on the global map), a source close to Cabello tells Billboard she was "completely blindsided” by the post on the official Fifth Harmony social channels (the group boasts 3.65 million Twitter followers and 7.5 million Facebook likes), which squarely put the onus of the departure on her. "This all [stems from] the girls' jealousy,” says the insider. "You've read this story a million times.”

What happened to precipitate a pre-emptive post by the four girls is a subject of some debate, although it seems there were a few attempts to structure a joint announcement -- ultimately unsuccessful. And it's not helping that Harmonizers are up in arms over leaked audio of group members complaining of being treated "like slaves." But by whom is also unclear.

"The whole thing was handled horribly,” says Los Angeles radio personality Chris Booker of AMP Radio, adding the caveat, "which, in 2016, is a very good thing because it's a headline -- that's the game now. If the remaining ladies of 'Fourth Harmony' say nice things, it's a nonstory.” Still, the veteran jock notes that a modicum of decency is called for in situations where a key member is exiting. Says Booker: "The right response from Fifth Harmony should have been, 'We love you, girl, we will miss you, go slay the world, blah, blah f---ing blah.'”

"It's very perilous to break up the winning team. I've seen it wreak havoc,” says Fair. At the same time, he adds, "Who's to stop the kid from taking a shot or forever regretting it? When it's not a marketing or a business decision but it's someone's hopes and dreams? The key is to manage the team and keep the train on the track. But who's to say Fifth Harmony as Fourth Harmony isn't a more robust, punchy proposition than it was with the extra spoke on the wheel? Today, the song is so dominant in the success recipe that as long as the girls and their team can continue to identify those great songs, they will be on top.”

For her part, Cabello has seemed quite deft at compartmentalizing the group's needs with her own career, telling Billboard back in February, "Fifth Harmony is amazing, that we can all come from different places and have different music tastes and have different ideas of what music we would like to make but all come together to be like, 'OK, this is our sound.' But at the end of the day, you feel kind of stifled when you can't completely express who you are without any compromises.” Learning to play guitar and being inspired by the likes of Ed Sheeran and John Mayer, she added, "This is who I am.” It's a sentiment echoed in her own statement the day after news of the split was revealed. "Be courageous in the pursuit of what makes your heart pound and what makes you come alive with purpose,” she wrote. "Our happiness is our own responsibility.”