A humbler, and actually probably less likely, theory about Sunset Shimmer · 8:59am May 20th, 2017
Remember the Reflections arc in the comics? Princess Celestia went back through the mirror to say a passionate and heartfelt goodbye to Good King Sombra after Starswirl found out; then she went back to say another passionate and heartfelt goodbye, and then to sob her heart out over what just happened to Luna, and then because she was so desperately lonely and had no one at all to talk to, and one thing led to another and suddenly it was a thousand years later and their two worlds were