Optimus Prime is searching for the truth about his Creators, and along the way he seems not to care about becoming a villain, going so far as to fight hand-to-hand against Bumblebee, as you can see in the trailer for Transformers: The Last Knight.
The Last Knight breaks the basic myths of the Transformers franchise and redefines what it means to be a hero. With Optimus Prime absent, a battle for survival has begun between the human race and the Transformers. The key to saving the future lies buried in the secrets of the past, in the hidden history of the Transformers in ancient times. Now the fate of the world falls on the shoulders of an unlikely alliance: Cade Yeager (protagonist of Age of Extinction), Bumblebee, Sir Edmund Burton (an astronomer and historian who knows the history of the Transformers), and Vivian Wembley (a professor at Oxford University), who must work together to discover why the Transformers keep coming back to Earth.
Apparently The Last Knight is about how the Transformers were members of King Arthur's Round Table, but now they are destroying Earth for unknown reasons. Optimus Prime is searching for the truth about his Creators and along the way seems not to care about switching to the villains' side, even fighting hand-to-hand against Bumblebee and the rest of his companions. In the video we can also see Hound, the Autobots' medic, in action, and a new Transformer called Dragonstorm, a member of the Knights of Cybertron that transforms into a three-headed mechanical dragon.
Without a doubt, The Last Knight marks a turn in the plot, where the hunted become heroes and the heroes become villains, in a dispute where the winner takes the world. This film features a cast led by Mark Wahlberg, Josh Duhamel, Tyrese Gibson, Anthony Hopkins, Laura Haddock, Isabella Moner, Stanley Tucci and John Turturro, among others. Produced by di Bonaventura Pictures and Hasbro Studios and directed by Michael Bay (Transformers: Age of Extinction), Transformers: The Last Knight will open in theaters in 2D, 3D and IMAX 3D on June 23, 2017.
Official site: Transformers: The Last Knight