The latest trailer for Star Wars: The Rise of Skywalker from D23 has added some new wrinkles by showing Rey dressed in black and wielding a double-bladed red lightsaber. We have a few theories as to what that could mean for the story, including that this is a clone of Rey rather than Rey herself. However, an evil Rey also fits nicely into my larger theory: what if both Rey and dark Rey both come from a batch of clones meant for a resurrected Emperor Palpatine to inhabit, but Rey somehow escaped or was stolen away by someone who left her on Jakku? And, combined with the revelation back in April that Palpatine is back and pulling strings, that fills in the mystery of who could’ve been behind this plot all along.
Source: IGN.com This Theory of Rey's True Origins Just Got a Little Stronger