Steven Moffat is undoing one of Doctor Who's cruellest twists - by bringing Osgood (Ingrid Oliver) back from the dead.
The loveable UNIT scientist will return for a new two-part adventure, alongside colleague Kate Stewart (Jemma Redgrave).
Osgood last featured in series 8's finale, 'Death in Heaven', and was killed by the maniacal Missy (Michelle Gomez).
Also returning to Doctor Who are classic monsters the Zygons, shape-shifting aliens first introduced in 1975 and last featured in 2013's 50th anniversary special, 'The Day of the Doctor'.
Moffat had previously expressed his desire to bring back the Zygons, following their reappearance in the celebratory episode.
Of Osgood's own return, he said: "Osgood is back, fresh from her recent murder at the end of last series. We recently confirmed that Osgood was definitely dead and not returning - but in a show about time travel, anything can happen.
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"The brilliant Ingrid Oliver is back in action. This time though, can the Doctor trust his number one fan?"
Written by Peter Harness - who scripted 'Kill the Moon' for series 8 - the new two-parter will feature a guest cast including Jaye Griffiths, Cleopatra Dickens, Sasha Dickens, Abhishek Singh, Todd Kramer, Jill Winternitz, Nicholas Asbury, Jack Parker and Aidan Cook.
Doctor Who will return to BBC One this autumn.
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