The shape-shifting race debuted in 1975's 'Terror of the Zygons' opposite Tom Baker's Fourth Doctor and will return in November's celebratory special.
The 3D special - expected to run 90 minutes - will star Matt Smith and David Tennant as the Eleventh and Tenth Doctors, plus companion actresses Jenna-Louise Coleman (Clara) and Billie Piper (Rose).
John Hurt (Alien) and Joanna Page (Gavin & Stacey) will also feature in the one-off, directed by Who veteran Nick Hurran.
Showrunner Steven Moffat previously indicated that the anniversary episode will not just be a "fanfest".
"We can't make this all about looking backwards," said the showrunner. "It's actually got to be the start of a new story."
Doctor Who continues this Saturday (April 6) at 6.15pm on BBC One with new episode 'The Rings of Akhaten'.
> Matt Smith on Doctor Who 50th: 'It celebrates old Doctors'
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Watch the stars of Doctor Who talk the 50th special with Digital Spy below: