You are Megatronus Prime, you and the other Primes were called to a meeting, only to be met with destruction, all of the other Primes were dead or injured, Sentinal was now working with the Quintisons, you were left on your own, luckily you were a very powerful Prime, and you were quite large too

I walked around in the ruins, seeing fallen Primes, it angered you, until you heard a cocky voice behind you

Sentinal Prime: Ah, there you are Megatronus, i admired you, but now it’s time to let you go…

He said standing in the hallway