When it comes to comic books, everyone's a detective. As if it would help the characters on the page, fans pore over every word and every panel looking for clues as to what's going to happen next. Through the power of the internet, these theories are then spread to the masses -- it's a necessary cycle. Marvel ends its comics with cliffhangers, as fans try to deduce what happens next before the next issue comes out. Sometimes, these things aren't even answered in the next issue. In some cases fans have to wait years for answers.

Things are no different on the movie side of things. Take Thanos, for example. What started as a fun little tease at the end of The Avengers has turned into one of the largest cinematic events ever. From the moment his grin was first shown, movie-goers began to predict the arrival of the Infinity Stones in the MCU. Then there are times where fan theories actually dictate the direction of the stories. Sometimes an idea put forth by someone outside the writers' room is so awesome that the powers that be can't help but include it into future installments. Let's look at 15 shocking Marvel fan theories that actually turned out to be true.

15 STAN LEE'S MCU CAMEOS MEAN MORE THAN YOU THINK

Stan Lee has shown up in just about every Marvel movie released in the last 20 years. Well, all except for that one Fantastic Four movie -- that lack of a cameo speaks volumes. Otherwise, we can always count on the creator of many of our most beloved characters to show his face on screen in some form or another. Fans have long theorized that his cameos must have a deeper meaning. Sure, these films exist in different continuities and Stan Lee himself even denied the rumor, but fans have a way of getting what the want.

It was James Gunn who finally caved. In a post-credits scene for Guardians of the Galaxy Vol 2., Stan Lee is shown telling stories to the Watchers. He isn't a Watcher himself an informant. It's a cool little way to show that the Marvel films are part of their own multiverse.

14 MISTY KNIGHT'S BIONIC ARM

The best thing about superhero TV is watching characters slowly grow into their comic book counterparts. Finally seeing Matt Murdock dawn his iconic red costume sent shivers down every fan's back. The same can be said for The Punisher spray painting that skull. We've watched Misty Knight kick butt through two awesome Netflix series. From the moment of her introduction, fans have been waiting to see her bionic arm and in the comics, it was Tony Stark who outfitted her with it.

Towards the end of The Defenders, Misty lost her arm. This was as much an Empire Strikes Back easter egg as a shout to her comic book persona. Thanks to a recently released press shot for Luke Cage season two, we know that Misty's bionic arm will be making its debut in all its glory.

13 HYDRA CAP WAS CREATED BY KOBIK

How do you sell more comic books? One proven way is taking one of your most beloved heroes and turning him into a villain. Though many were outraged by Steve Rogers uttering "Hail Hydra," the publicity stunt worked. Captain America held comic book headlines for months.

Marvel swore up and down that there was no trickery afoot. This was the real Steve, simply coming out of hiding after years under cover. Fans were not so easily duped, and many deduced that this switch must be the work of Kobik -- it turns out they were right. Kobik not only messed with Cap's brain, but actually created an entirely different timeline and universe centered around her beliefs that Hydra was the right way to live. Then she sent the real Cap back to punch the other guy in the face.

12 LOGAN'S DEATH PREDICTION

For better or worse, Wolverine now has a complete film trilogy all his own. While X-Men Origins: Wolverine was poorly received by just about everybody, the second installment performed much better. The Wolverine returned the character to his former glory. It introduced some cool adaptations of other comic book mutants.

One of these characters is Yukio, a mutant capable of predicting the deaths of others. At one point, she has a pretty specific vision of Logan dying. Spoiler alert: he does actually die in Logan. While the circumstances of the prediction aren't exactly the same, the are very similar with one notable exception: Yukio tells Logan that he'll die with his heart in hand. He doesn't die holding his literal heart, but the hand of his daughter. Director James Mangold confirmed via Twitter that this payoff was his exact intention all along.

11 THE ORIGINAL GUARDIANS IN VOL. 2

James Gunn does love his fans. Comic book fans are no strangers to easter eggs in their films, and Gunn has supplied some of the best ones. From Howard the Duck to Adam Warlock, many of Marvel's lesser known characters are on full display the the Guardians of the Galaxy films.

When Sylvester Stallone was cast in the sequel, fans began to speculate on his role straight away. The prevailing theory was that he would play a member of the original comic book Guardians lineup. This theory turned out to be bang on. Yondu had already appeared in the first film, but this time around, fans got to see the entire original lineup. Charlie 27, Aleta Ogord, Martinex, Mainframe and Stallone's Starhawk are all shown together in yet another post-credit scene.

10 SPIDER-MAN'S MCU DEBUT

For a while, it seemed like there was no hope of Peter Parker showing up in the MCU. Sony were forging ahead with their own plans for a web-head based extended universe while Marvel was forced to build their universe without their most popular character.

Everything changed after the release of The Amazing Spider-Man 2. Suddenly, Captain America: Civil War was on Marvel's release slate and it seemed like Spider-Man was well and truly home. The thing is, Marvel always plays the long game. Fans have long speculated that one little boy in an Iron Man mask in Iron Man 2 was a young Spider -- Tom Holland recently confirmed this to be true. It doesn't change much, but it's a fun way to show that Spider-Man has been around since the beginning.

9 ASGARD'S MCU DESTRUCTION

There were many theories as to how Thor: Ragnarok would end. Many of them came true in some form or another. Loki was kind of responsible for Hela's release. Thor and Doctor Strange sort of work with Loki to find Odin on Earth.

The most prominent (and accurate) theory was born all the way back when Avengers: Age of Ultron was released. During a hallucination, Heimdall tells Thor that he will be responsible for Ragnarok. In Norse mythology, Ragnarok is the destruction of all things. The theory became that Asgard would be gone by the end of the third Thor film. While the manner of its destruction was not what many thought, and not at all what it was in the comic of the same name, the end result was the same: Asgard now lies in ruins.

8 WHY THE FANTASTIC FOUR COMICS WERE CANCELLED

This is a dark one. Marvel's first family have been instrumental in their comic book events for years. Their film presence has been decidedly less important. When Marvel were forced to sell the film rights to many of their most popular characters to stay afloat, Fox eagerly lapped up the Fantastic Four.

Since then, Fox has been releasing one stinker after another in the Richards family name. By the time the 2015 reboot rolled around, Marvel Comics had all but phased the characters out. Though fans (and media) continued to speculate, Marvel denied any connection to the film conundrum. They changed their tune recently. Writers Jonathan Hickman and John Barber confirmed it in a recent interview, as Barber bluntly put it "three BLEEPING terrible movies don't help anything."

7 SKYE'S REAL NAME

Agents of S.H.I.E.L.D. bringing Phil Coulson back to life was a big deal. This was the first guy the Avengers had to avenge after all. But from the beginning, fans' focus was clearly elsewhere. That honor went to the feisty hacker Skye, a character not appearing in any comic book.

During season two, Skye's father was slowly revealed to be the classic comic villain Mister Hyde. Fans began putting the pieces together immediately. In the comics, Mister Hyde is the father of Daisy Johnson, better known as Quake. The theory had more weight because Skye had reacted positively to a solution called GH.325 made from the blood of a blue alien. That alien was revealed to be a Kree, and Skye was revealed to be the Inhuman known as Daisy Johnson before the second season was over.

6 THE NINJA TURTLES DAREDEVIL CONNECTION

The Teenage Mutant Ninja Turtles started off as a joke. Comic duo Kevin Eastman and Peter Laird spent a night in 1983 trying to outdo each other with silly sketches. The more they joked, the more awesome the concept became. That night, the Turtles were born. The joke continues in the Turtles' origin story. The panels show a container of ooze hit a blind guy in the face. After that, it explodes all over four innocent turtles and a rat. We all know who the animals turned out to be, but who was that blind guy?

This one was actually never all that secret, but since the turtles and Daredevil are owned by different companies, a real crossover has never happened. It's a connection that Eastman and Laird have confirmed on many occasions though.

5 THE EYE OF AGAMOTTO

Leading up to the release of Doctor Strange, only four of the six Infinity Stones were accounted for.  Fans obviously took to the internet to speculate as to where the Time Stone and the Soul Stone could be. A popular theory soon arose that the film would give us the Time Stone. The theory made perfect sense. Doctor Strange was going to introduce magic into the MCU. What better setting to throw an Infinity Stone into? Couple that with the film's tripped out visual style and you have a slam dunk.

The theory turned out to be perfectly accurate. The Eye of Agamotto, a popular item of Strange's from the comics, houses the Time Stone. Not only that, but the stone's powers were instrumental in the films final confrontation between Strange and Dormammu.

4 VALKYRIE IS A BISEXUAL

There are a lot of groups Hollywood has largely ignored over the decades. Over the last couple of years, that's finally started to change. Wonder Woman was the first (good) female superhero movie. Black Panther recently became the first big budget film with a predominantly black cast. One area that's developed arguably slower than others has been the inclusion of LGBTQ characters. That's not to say that no progress has been made whatsoever. One scene in Thor: Ragnarok showed a fellow female soldier sacrificing herself for Valkyrie. The brief look exchanged showed that they were more than just coworkers.

While it wasn't stated in the film, Tessa Thomson confirmed the character's sexual orientation. A deleted scene provided further proof. It's not what many were hoping for, but the character is set to appear in future films -- that door is more than open.

3 KILGRAVE IN JESSICA JONES SEASON 2

Jessica Jones season one was awesome. Krysten Ritter's portrayal of the titular character had a lot to do with that. But the show wouldn't have been the success that it was without David Tennant's unhinged villain Kilgrave. Unfortunately, (for us, not for Jessica) Kilgrave was killed in the final episode. So was David Tennant done with the show? Fans immediately began to think otherwise. Such a powerful character would surely make a return, but coming back from the dead is no small feat though, and the Netflix side of things is much more grounded in reality than the films.

Fortunately, set photos quickly assuaged fans' concerns. Kilgrave will indeed be making his presence known. At the time or writing the show has yet to be released, but he will likely be tormening Jones through flashbacks.

2 THE QUANTUM REALM IN DOCTOR STRANGE

Fan theories, so many fan theories. As the MCU has continued to grow, so has its followers' hunger for knowledge. Especially when a film promises to reveal a side of the universe not yet seen. Let's take a look at a theory that began all the way back at the end of Phase Two. Ant-Man was hilarious and lighthearted, but it still managed to reveal a whole lot about the history of the MCU. It also gave us our first look into the quantum realm (and a tragic story to go with it).

When the trailer for Doctor Strange was released, many theorized that this realm would make a return. It fit the visual aesthetic of the film. Sure enough, in order to open Strange's mind, the ancient one takes him on a journey through many other realms. The Quantum Realm happens to be one of them.

1 ONE BIG MARVEL DC MULTIVERSE

In the '90s, Marvel and DC comics collaborated more frequently. It wasn't all that uncommon for Spider-Man to pop over to Gotham City to help Batman with a case. Or for Wally West to have a race with Pietro Maximoff to determine the faster speedster (Wally is faster). During the last couple of decades, those crossovers have lessened. As the two companies have fought for cinematic universe supremacy, they have stayed away from each other's work. Still, fans have always thought that the two multiverses must be one and the same.

This speculation was recently confirmed. In Infinity Countdown Prime #1 we got a glimpse of the first Captain Marvel. Not Mar-vell, but the super hero currently known as Shazam. DC responded in Action Comics by referencing an Alfred from another timeline named Jarvis.