Petronella Osgood worked for UNIT along with Kate Stewart. She assisted the Eleventh Doctor when Earth was under threat from the Zygons and acquired a Zygon double, whom she came to regard as her sister. The Doctor secretly put the two Osgoods in charge of keeping the peace between humans and Zygons. One of the Osgoods was killed by Missy, and the other, refusing to reveal whether she was human or Zygon, helped the Twelfth Doctor defeat a Zygon uprising. Bonnie subsequently took the form of Osgood so they could be a pair again.
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