This is how To the Core goes in Connor Lacey's Super Adventures of Transformers: War for Cybertron.
Narrator: HAVING EMBRACED HIS DESTINY AS LEADER OF THE AUTOBOTS, OPTIMUS PRIME LEADS A SMALL BAND OF AUTOBOTS TO SAVE THE CORE OF CYBERTRON ITSELF FROM THE CLUTCHES OF MEGATRON. BUT TO DO SO, THEY MUST FIRST RESCUE THE MIGHTIEST AUTOBOT GUARDIAN EVER CREATED–OMEGA SUPREME.