all right, so I've watched the trailer for the last knight multiple times since it was released, and thanks to the upload of the screen caps, I was able to get some decent pictures to help with this theory! so let's start off with that ominous planet like thing we see hovering over the moon.
if it isn't him, it is at the very least a nod to our favorite giant orange world devourer, unicron. short beginning but anyways, now on the the part i'm looking forward to, whether or not the optimus we see battling bumblebee is the same optimus we see deactivated in space!

here are two pictures where we see optimus prime right as he reactivates in space.



Note how battered and worn optimus looks, plus the blue eyes. now let's take a look at some pictures of the optimus we see battle bumblebee.




It doesn't take long to notice optimus certainly wasn't like this when he reactivated in space, plus his weapons are nowhere to be seen, and let's not forget the purple eyes. either he somehow repaired himself and discarded his weapons before becoming corrupted by whatever is wrong with him, or this is a clone created by the baddy of this film that has been warped so badly, he believes that he is doing this against his will. well, that's about it, oh and if you watch closely at the end of the trailer, bumblebee attempts to catch his arm before it cuts to black. hope you like this

 

He's the same guy. Especially if he's asking for forgiveness. He looks like they (whoever they are cough* Quints cough* repaired him but tampered with his head (scar on his face)

 

That makes sense, but my theory could definitely work as well! But I Guess we'll know the truth in a few months, right?

 

We don't know the full context of the "Forgive me" line, though.
Heck, it might even be another one of those lines that we hear in the trailer but not in the movie.

 

Definitely could be, I've seen that happen with a couple movies!

 

I swear I see a face in the center of unicron (?)