'Transformers 5' release date, spoilers: Why is Optimus Prime battling the Autobots?

Paramount Pictures has finally released the trailer for "Transformers: The Last Knight" and the visual effects were top-notch. As shown in the trailer, the film is going to take viewers through the ages. In one scene, a three-headed mechanical dragon is flying overhead, and in another, a group of medieval knights gets blown to smithereens. It looks like the Nazis are going to meet the Transformers, too.

While those scenes are undoubtedly intriguing, one particular sequence made people wonder. Why in the world is Optimus Prime (voiced by Peter Cullen) fighting Bumblebee? What happened to Prime while he was floating around in space? It looked like he was dead.

Well, a couple of theories have come up since the trailer was shown. The first one involves the other big reveal — Unicron. Actually, it hasn't been confirmed that the mechanical planet that was trying to eat the moon in the trailer was Unicron, but fans believe that no other character fits the description.

Anyone who has seen the '80s animated film "The Transformers: The Movie" would know that Unicron has the ability to create new bodies for Transformers who were on the brink of death.

He transformed Megatron into Galvatron in the animated film, so it's possible that the film version of Unicron will do the same thing with the seemingly lifeless body of Prime. Fans may also notice that Prime's eyes were purple, not the usual blue. Perhaps he's under some sort of mind control.

Cosmic Book News also noted that fans may see the Quintessons in "The Last Knight." In the '80s animated series "The Transformers," the multi-faced creatures revived Prime as a mindless "zombie" to battle the Autobots. So, maybe they are behind the evil Prime.

Will fans see Unicron and the Quintessons in "Transformers: The Last Knight"? Find out when the film premieres on June 23, 2017.