The premise of Once Upon a Time is one that could - and should - have made for a truly enjoyable series: your favorite fairytale characters have come to life in the modern world.

However, thanks to countless bad plotting choices, the repeated use of inane memory wipes, unsympathetic characters, and much more, the series lost its way from its promising start early on to become a muddled mess.

Seven seasons in, the series is hardly anything like it once was, with the majority of its original cast having exited the series after season six. However, in those first six years, the cast tried their best to produce something that would be enjoyable and real, even as the writing suffered.

During those seasons, a whole lot of behind the scenes drama went down as well, which stands in stark contrast to the hopeful message of the series. No matter how sunshiny and pure these fairytale characters may seem, there's no controlling what their actors and creators could do at any given time.

Here are the 15 Dark Secrets You Never Knew About Once Upon A Time.

15. Jennifer Morrison and Lana Parrilla allegedly feuded behind the scenes

It's hardly ever a guarantee that co-stars are going to get along. Celebrity feuds aren't exactly a new concept, and in this day and age of social media and convention circuits, spats can get pretty out of hand pretty fast.

However, in the case of Jennifer Morrison and Lana Parrilla, their mutual dislike has been more of an open secret within the show's fandom for years.

The Once cast is a remarkably close one, with many true lifelong friendships having been formed within the ranks. Morrison and Parrilla, however, are decidedly not part of that trend. Rarely ever taking a photo together or engaging in any joint events or interviews, the duo are also pitted against one another by the fans.

Some eagle-eyed viewers have even pointed out that certain scenes between the two clearly use body doubles, which really says it all when it comes to their inability to tolerate one another.

14. Emilie De Ravin and Tom Ellis have been accused of cheating together

Relationships that bloom on set between co-stars are a fairly common phenomenon when it comes to movies and TV shows, regardless of whether they're successful relationships or not.

Unfortunately, though, infidelity on set is something else that happens all too frequently. In the case of Once Upon a Time, a sordid wrinkle in its production history comes in the form of an encounter between a series regular and a guest star.

Tamzin Outhwaite, ex-wife of Lucifer star Tom Ellis, has alleged that Ellis cheated on her with Once's Emilie De Ravin during the one episode in which he appeared as the original Robin Hood.

Perhaps Ellis's replacement in the role is now something that will be more easily understood by fans.

13. Josh Dallas and Ginnifer Goodwin's unconventional relationship beginning

In the world of Once Upon a Time, Snow White and Prince Charming are heralded as the epitome of True Love. A couple who will always find each other no matter the odds that may be facing them, they survived evil curses, memory wipes, dragons, and so much more.

In reality, co-stars Ginnifer Goodwin and Josh Dallas have forged their own true love story, but theirs had a far less fairytale type beginning. When Goodwin and Dallas met at the beginning of Once's production, Goodwin was still engaged to her fiance Joey Kern, and Dallas was married to his then wife Lara Pulver.

However, Dallas and Goodwin are now, much like their onscreen counterparts, married with two kids.

12. Sebastian Stan's Mad Hatter was meant to be a much bigger role

In one of Once's strongest episodes, "Hat Trick," viewers are introduced to the absolutely magnetic character of Jefferson, as played by Sebastian Stan.

Jefferson is one of the only characters in all of Storybrooke who has been allowed to retain his memories of life in the Enchanted Forest - a world in which he was The Mad Hatter and lived with his young daughter, Grace.

Thanks to Stan's perfomance, Jefferson's anguish and trauma are treated as raw and real and tragic. His arc over the course of that one episode ranges from sympathetic to villainous and back again. Later episodes find him reuniting with his daughter after all this time, but after they reunite, he's never seen again.

As it turns out, much more was meant to come from Jefferson's character, but Sebastian Stan's busy schedule - thanks in large part to his commitment to the MCU as Bucky Barnes - prevented the character from returning.

11. Stan's MCU success may have ended his relationship with Jennifer Morrison

It may not have only been Jefferson's return to Once Upon a Time that Stan's success within the MCU prevented, however.

According to reports at the time, the relationship between Jennifer Morrison and Sebastian Stan came to an end in 2013 due to the co-stars-turned-couple having to deal with distance and different schedules that caused a rift between the two.

All reports on their breakup stressed that the couple, who had dated for a little more than a year from 2012 until 2013, had no hard feelings toward one another.

So unfortunate though it may be, it really does seem as though the gain of Stan's Bucky led to the loss of the wonderful relationship he shared with Morrison.

10. Hook was meant to be a character from the start, but it got complicated

For better or worse, it's hard to imagine what Once Upon a Time would have looked like had Captain Hook not joined the cast of characters in the series' second season.

However, as it turns out, if the showrunners Eddie Kitsis and Adam Horowitz had their way, Hook would have been an original member of the cast from the very beginning.

As they've explained in various interviews and convention appearances, his character was meant to be incorporated in the first season, but acquiring the rights to J.M. Barrie's character proved to be an issue.

They maintain that his character was always meant to be a central one, and that he was always designed as the true love for Emma Swan's savior character as well.

9. Sean Maguire has been openly critical of the show's treatment of Robin Hood

One of the many problems with Once over the years is the way in which its focus shifts from character to character in a truly uneven way. As a result of this constantly shifting prioritization, some characters never receive the development they're due.

Robin Hood is perhaps the clearest case of this. An originally spark-filled character with an interesting personality and backstory in the third season, Robin soon became no more than a love interest for Regina. In some episodes, he scarcely ever said a word, lingering in the backgrounds as glorified human scenery.

Actor Sean Maguire has been vocal about his unhappiness with the way the show treated his character, especially given the brutal and unceremonious death his character was given at the hands of the Greek god Hades.

8. Meghan Ory was promoted for a major arc in season 2, but the show never delivered so she left

The character of Ruby Lucas offered what was arguably one of Once's most successful and most interesting fairytale adaptations: Little Red Riding Hood, it turned out, was the Big Bad Wolf all along. An extremely independent and strong character, Ruby's personality added a fun dash of spark in every scene she had, no matter her scene partner.

So it made sense, then, that the series promoted her portrayer, Meghan Ory, to series regular in season two. Ruby was supposed to receive a much bigger plot, and in the first half of the season, it started to show in her relationship with Charming.

However, suddenly, plans for the second half of the season changed, according to Ory's recollection at the time, and Ruby was mostly absent from the later episodes.

And after that season, Ory herself would walk away from the show, only returning for a handful of episodes in the seasons to follow.

7. Zelena was only introduced because the showrunners liked working with Rebecca Mader

Prior to working on Once Upon a Time, Kitsis and Horowitz spent some years working on another maddening and often disappointing series, Lost.

During their time on the series, Rebecca Mader was cast as Charlotte Lewis, anthropologist and love interest of the enigmatic physicist Daniel Faraday.

Kitsis and Horowitz so enjoyed working with Mader on LOST that they decided they needed to find a character on Once that would be well-suited for her. Eventually, they settled on Zelena, who had a short arc in season three as the seasonal primary antagonist Wicked Witch.

Yet since they enjoyed Mader so much, she would return to the show and became a main character, even as Zelena rarely offered anything of substance to the overall plot.

6. Rumpelstiltskin was written for Robert Carlyle, even though they never expected to cast him

When writing for a piece of media, it's pretty hard not to mentally cast the dream actor you imagine in a role. It makes it that much more easier to hear and understand the character's voice and behavior when you have an audiovisual reference, after all.

So as they adapted their version of Rumpelstiltskin, Kitsis and Horowitz found themselves returning again and again to the actor Robert Carlyle as the only person they could imagine in the role. But never did they ever believe that he would be willing to take on the character, even if he was the only one they wanted for the role.

But now, seven years later, Carlyle is one of the only original cast members who remains with the series, proving that even a writer's wildest dreams can come true in Hollywood.

5. Lady Gaga was seriously considered for the Blue Fairy

Sometimes, stunt casting is okay. Enjoyable cameos can liven up any episode, whether comedic or dramatic. But in other cases, stunt casting is the worst possible thing a series could do, especially when it involves a frequently recurring role.

Thankfully, Once avoided this misstep, though not through any of their own original planning. According to Kitsis and Horowitz, Lady Gaga was the actress they originally intended to have star as the perpetually shifty Blue Fairy. They even reached out to her management with the offer of the role when the series began in 2011.

But they never heard back, and never even knew if the offer had reached her, so Gaga never set foot in the Enchanted Forest.

4. Multiple stars were harassed by fans to the point of leaving social media

Fans can get pretty passionate when they're invested in a series, whether it's a movie franchise or a television show. In the age of social media interactivity, however, that fan passion can get out of hand and lead to some really destructive behavior.

In the case of the Once Upon a Time cast, there have been at least three incidents in which fan harassment led actors to withdraw from social media. After being harassed by a particular group of fans, Ginnifer Goodwin deleted her Twitter profile and has never returned. Josh Dallas was harassed by troll accounts on Twitter and Instagram and deleted his pages, but has since taken up Instagram again after roughly a year away.

Jennifer Morrison also withdrew from using Twitter in any form after the first three and a half seasons of the show, in which she had frequently engaged in fan Q&As. Now that she has left the struggling series, however, she has become much more active.

3. Parrilla made the writers change the Regina/Henry dynamic, and made that part of the show not make sense

For the first two seasons of the show, the relationship between Evil Queen Regina and her adoptive son Henry is consistently framed as abusive. She gaslights him into believing he's crazy, wipes his memories, and forces him to love her.

She leaves him suspended in midair with tree vines when he dares to rebel against her abusive ways. And as if that all wasn't bad enough, she poisons him with a lethal dose of a magic potion intended for his birth mother, Emma.

But sometime during the second season, Parrilla felt the need to convince the showrunners that framing a villain, as a villain, equated the writing of their dynamic to bad representation of an adoptive relationship.

Never minding the fact that season three reveals that he was illegally adopted, the bizarre twist of perspective on their relationship created a muddled mess that shortchanged many of the series' far healthier dynamics.

2. Katee Sackhoff auditioned five times for the role of Emma Swan

There's no question about the fact that Emma Swan is the beating heart of Once Upon a Time to its many devoted fans. The absence of her character in the show's poorly conceived reboot season is palpable and uncomfortable to most if not all fans.

Much of what made Emma such a significant and inspiring character can be attributed to Jennifer Morrison's spot-on portrayal of the lost girl who found home.

From the moment they auditioned her for the part, the series' showrunners knew that they wanted Morrison for the role above all else. But even despite their conviction regarding their dream casting, auditions continued, even including a five round audition process for sci-fi fan favorite Katee Sackhoff.

1. Prince Charming was meant to die (and stay dead) in the pilot

It's a truly heartbreaking moment in the pilot episode of the Once Upon A Time when Prince Charming valiantly sacrifices himself in order to save his newborn daughter Emma.

As he seemingly dies within the world of the Enchanted Forest, viewers are left hanging... until it's revealed that he managed to survive the near death experience and is in Storybrooke in a coma.

However, according to the original idea for the series, things were almost a whole lot darker: Prince Charming was never actually meant to survive his ultimate hero's sacrifice moment. In fact, he was meant to meet certain death.

For a show ostensibly about hope, this early death may have struck too bleak a note for the beginning of its many tales.

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What other dark secrets from Once Upon A Time do you know? Let us know in the comments!