Optimus's lost twin

What if Optimus has a twin and no one knew about it? not even him?
Nebula was always a bright Sparkling. she shared traits with her twin, Orion, and never got in strife with their creators. then the Fallen Prime Megatronus started stealing bots for his cause, including Nebula.
she is raised by Megatronus as a cold blood thirsty killer, and remembers nothing of how Megatronus Prime got her, only that she was saved from death. she hears about an uprising on Cybertron and the Decepticons are formed. she is sent by Megatronus to join the Decepticons cause, and join she did.
she then realises that her spark is shared with someone that gets into way more fights than her, and 4 thousand millennia later, she may find her answer on a planet called Earth