The overthrow of Emperor Philippa Georgiou of the Terran Empire in 2257 during a coup by Gabriel Lorca aboard the palace ship ISS Charon, which ended with her exile in the prime universe.
In the mirror universe Georgiou ruled the Terran Empire from the ISS Charon, a vast ship powered by a captive mycelial reactor. Her former protege Gabriel Lorca had already tried once to unseat her and had fled to the prime universe, where he took command of the USS Discovery.
In Vaulting Ambition and What's Past Is Prologue Lorca returns with Michael Burnham, frees his followers from the agony booths and takes the throne room. Burnham sides with the Emperor, and Georgiou kills Lorca. With her authority broken, she prepares to die fighting, but Burnham beams her to Discovery as the Charon is destroyed.
Georgiou could not go home. She was later recruited by Section 31, and her loss of the throne shapes her story through three seasons of Discovery.