In this series, Megatron is killed but eventually comes back to life. However, in the first season until the season finale, Megatron has a hallucination in Optimus Prime's head, similar to Kessler, from The Boys, taunting him and causing Optimus to have periodic panic attacks. Essentially, there will be an episode that's a flashback to the moment Prime killed Megatron, but in the season finale, Megatron will return, thus once again becoming the big bad for the remainder of the series until the series finale.