What some of us believe is that the Gold-Bot from the trailer is Sentinel Prime, which I also believe. Another thing, which complicates things, is of how the Fallen could have been released as Optimus was the last Prime. Kinda doesn’t make sense now, huh? Don't jump first about loop holes - My idea is that Sentinel (who can be counted as a descendant of the Primes), and all of those other Transformers that were either dead or deactivated on the Ark that were discovered by Buzz Aldrin and Niel Armstrong, were and could be counted as "dead" in the ritual of the Fallen's rising again. Then, two years later after ROTF, DOTM takes place and Sentinel comes back (from "statis lock"), present day?