Once Upon a TimeWas Optimus Prime a member of King Arthur's court? It's possible, since "Transformers: The Last Knight" is adding King Arthur to the mix.

"Once Upon a Time."

"Last Knight" reportedly ties into Arthurian legend, and Arthur and Merlin will both be involved in the story in some way (Santiago Cabrera is playing the wizard). The Transformers have been around on Earth since prehistoric times, so it's entirely possible they got mixed up with the knights of the Round Table. Maybe Optimus Prime helped Arthur take Excalibur out of that stone?

Mark Wahlberg stars once again as inventor Cade Yaeger, and Tyrese Gibson and Josh Duhamel are returning to the fold. They'll be joined by Oscar winner Anthony Hopkins.

"Transformers: The Last Knight" is set to open in theaters June 23, 2017.

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