Mother and daughter Dame Diana Rigg and Rachael Stirling are to star side by side in a Doctor Who adventure to be broadcast next year.
It is the first time the pair have worked together on screen.
The actresses will play “a mother and daughter with a dark secret” alongside Matt Smith, as the Doctor, and new companion Jenna-Louise Coleman.
Filming began this week at Roath Lock Studios in Cardiff.
Dame Diana Rigg, who played Emma Peel in The Avengers in the 1960s, will play “a Yorkshire local”.
She said: “The first time Rachie and I will be working together is on an episode of Doctor Who specially written for us by Mark Gatiss. How lucky is that?”
Rachael Stirling said she was “looking forward to the madness of Doctor Who enormously”.
“Mark Gatiss has written a gift of a script and an on-screen relationship between Ma and I that is truly delicious.
“We have never before worked together because the offers have not been tempting, but when such a funny and original script comes through you know the time has come.”
Stirling’s TV work includes Women In Love and Tipping the Velvet.
Doctor Who’s executive producer Steven Moffat said: “Dame Diana Rigg, Rachael Stirling and a Mark Gatiss script – a combination of talents you could only get in Doctor Who! Frankly, I’m terrified already!”
2013 will be the 50th anniversary of Doctor Who, which was first broadcast in November 1963.