The Zygon Inversion (in-universe)

The Zygon Inversion was the eighth episode of the ninth series of Doctor Who. It followed The Zygon Invasion and was succeeded by Sleep No More.

It featured The Doctor, Clara, Osgood and an individual resembling Kate Stewart. Its synopsis mentioned that "with UNIT neutralised, only the Doctor stands in the way..." By 10 May 2020, the episode was available on BBC iPlayer along with the rest of series 9. (WC: The Zygon Isolation)

Important note
This is a in-universe counterpart of the real world Doctor Who television story The Zygon Inversion that exists within the Doctor's universe. It was a visual meta-fictional cameo in The Zygon Isolation, where Petronella Osgood and her Zygon duplicate scroll through BBC iPlayer searching for something to watch.