"Can the Doctor trust his number one fan?"

Remember the Doctor-obsessed Osgood (Ingrid Oliver), who previously appeared in Day of the Doctor and later Death in Heaven? Well, she's back!

She may be back with a minor costume variation that resembles the Seventh Doctor's jumper, but we are all wondering - how? We previously saw Missy (Michelle Gomez) turn her into a pile of ashes during a Cyberman invasion. Steven Moffat has stated "We recently confirmed that Osgood was definitely dead and not returning - but in a show about time travel, anything can happen. The brilliant Ingrid Oliver is back in action. This time though, can the Doctor trust his number one fan?".

Not only will Osgood be back, but the Zygons (last seen in the 50th anniversary special) are too! During the feature-length episode, Osgood (as well as two other UNIT members) were duplicated, with both sides forgetting who were human and who were Zygon, perhaps this is the resolution to that part of the story?

Actress Ingrid Oliver commented on set “As every actor who’s worked on Doctor Who will tell you, there’s always the secret hope you'll get the call asking you to come back. To actually receive that call is both unexpected and brilliant. The word ‘honour’ gets banded about a lot, but it really is, it’s an honour. Especially because I was so sure Osgood was a goner after the last series!”

The two-part episode is currently being filmed in Cardiff and is written by Peter Harness (Kill the Moon), produced by Peter Bennett and directed by Daniel Nettheim.

Also joining Peter Capaldi (The Doctor) and Jenna Coleman (Clara Oswald) and confirmed for guest roles in the double episode is Jemma Redgrave, Jaye Griffiths, Cleopatra Dickens, Sasha Dickens, Abhishek Singh, Todd Kramer, Jill Winternitz, Nicholas Asbury, Jack Parker and Aidan Cook.

Doctor Who series nine will be back on BBC One in Autumn 2015