A couple months ago there was a rumor that a grey prototype that no one could recognize or could even guess at may be a new toyline addition for the Transformers Universe. There were guesses all over the map, from War Within Grimlock to TransTech Optimus Prime.
Thanks to the latest trailer for the recently discovered War For Cybertron game, we can now deduce that one of the said unknown prototypes may, in fact, be that of Optimus Prime.
As of posting, we can neither confirm nor deny the complete validity of this revelation, but the images don't lie and it looks like the Transformers Universe may be getting new additions to the family.