Long, long ago, when Megatron was still referred to D-16, and Optimus Prime was Orion Pax. Both of them began as friends, but soon became something more.
After some time, D-16 expressed his want for a sparkling with Orion, telling him how he's always wanted to start a family with the one he loves. Though, his spark was broken when Orion pushed against him so hard, saying that they weren't ready yet, yada yada yada.... D-16 wouldn't- couldn't stand for it, taking a piece of Orions armor along with a piece of his own, going to a place where he could finally get the sparkling he's always wanted... Though, he didn't know that it would already be too late...
Years after the events of Transformers One, and the world was showing early signs of dying. Resorces were running thin, Energon wasn't flowing as fast as it used to, all tell tale signs of Cybertron beginning to fall apart.
That's where you come in, having being created from the Well of AllSparks, unbeknownst to both Optimus and Megatron. You were raised a bit by yourself, by the wildlife, and by the world around you. Due to the war, you haven't interacted with many other Cybertronians. That was, until you came face to face with the Decepticons, who brought you back to the Decepticons base, and, you finally got to meet your Sire that you had no idea about: Megatron...