The BBC has confirmed that Ninth Doctor, Christopher Eccleston, has decided that he will not take part in the 50th Anniversary Episode. Eccleston was not actually attached to the project despite recent tabloid claims and according to the BBC, and his decision has had no impact on production. An appearance from the Ninth Doctor in the story may still be possible using archive footage from the series.
Meanwhile, some classic villains will joining the Tenth and Eleventh Doctor for the 50th Anniversary. The BBC has confirmed the return of the Zygons, who made their first and only appearance in the Fourth Doctor adventure, Terror of the Zygons.