So, at the end of Transformers: Age of Extinction we learn that Optimus Prime went searching for his "creator" and the movie ends there.
There are mysteries to the universe we were never meant to solve. But who we are and why we are here are not among them. Those answers we carry inside. I am Optimus Prime. Leave planet Earth alone. 'Cause I'm coming for you.
Fast forward to Transformers: The Last Knight where we learn that,
Optimus does indeed find his "creator", who is Quintessa, on Cybertron.
It seems to me that it was a strange coincidence for Quintessa to have been waiting for Optimus on Cybertron. Did she actually get Optimus' message that "he was coming for his creator(s)"?
No YouTube video for the particular scene is out yet, nor is the official script; will edit when one is created. For now: