"I've been living in this franchise for over 10 years now. For Transformers: The Last Knight, we put together a writers' room designed to greatly expand our mythology, integrating our films in a whole new way," Bay's letter begins. "Every movie will interlink. It was a huge task to expand mythology from the beginning of the world throughout history."
Bay wrote that the following writers were brought on board to help: Akiva Goldsman, Geneva Robertson-Dworet, Christina Hodson, Andrew Barrer and Gabriel Ferrari, Steven DeKnight, Art Marcum and Matt Holloway, Ken Nolan, Zak Penn, Lindsey Beer, and Jeff Pinkner.
"Through the summer of 2015, they worked in a huge space on the Paramount lot, surrounded by over 10,000 concept images from the franchise's history: the movies, cartoons, and comic books," Bay wrote. "They had a life-size Bumblebee, a Megatron head, and many other props staring them down. We pulled from everything. It was a fan's dream room.
"We brought in Transformers historians from Hasbro to educate them on where Transformers has been – so that they could figure out where it can go."
Bay hinted at his time with the franchise nearing an end, as he's wont to whenever one of them comes out.
"It's bittersweet for me. With every Transformers film, I've said it would be my last," Bay wrote. "I see the 120 million fans around the world who see these movies, the huge theme park lines to the ride and the amazing Make- A-Wish kids who visit my sets, and it somehow keeps drawing me back. I love doing these movies. This film was especially fun to shoot. But, this time might really be it. So I'm blowing this one out."
The letter ends in somewhat of a dramatic fashion, stating: "There comes a moment in everyone's life when we are called upon to make a difference.
"In Transformers: The Last Knight, the hunted will become heroes. Heroes will become villains. Only one world will survive: theirs, or ours."
The letter also provides a synopsis for the film:
The Last Knight shatters the core myths of the Transformers franchise, and redefines what it means to be a hero. Humans and Transformers are at war, Optimus Prime is gone. The key to saving our future lies buried in the secrets of the past, in the hidden history of Transformers on Earth. Saving our world falls upon the shoulders of an unlikely alliance: Cade Yeager (Mark Wahlberg); Bumblebee; an English Lord (Sir Anthony Hopkins); and an Oxford Professor (Laura Haddock).
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Transformers: The Last Knight is set for release June 23, 2017.