Even though this is being sold as a Bumblebee solo movie, Optimus Prime will be in the movie.
It has yet to be revealed exactly how much, or in what fashion, Optimus Prime is going to show up in this Bumblebee spin-off, but he’s definitely going to be in it.
He was recently asked if Optimus Prime is going to show up in the movie while being interview by Cinemovie.
Peter Cullen, who voices Optimus Prime in the live-action movies, as well as the cartoons in the 80s, has been promoting the home video release for Transformers: The Last Knight.