The Daemons - S8-E5
Trivia: The helicopter that explodes into flames and crashes in this episode was simply a piece of stock footage taken from the 1963 James Bond movie From Russia with Love.
Doctor Who (1963)
1 trivia entry for season 8
Revealing mistake: (Ep. 4) After Omega takes off his mask and looks in the mirror, when he sees that his physical body doesn't exist he puts his mask back on and screams, but when he shouts, "If I exist only by my will, then my will is to destroy," Omega's mask pops up off his face, and we can see the actor's blackened face as he shouts the last bit of his dialogue. (00:07:10)
The Doctor: This is a situation that requires tact and finesse. Fortunately, I am blessed with both.
Question: What caused the first Doctor to regenerate? Was it old age?
Chosen answer: No, it was the result of the Cybermen's draining Earth of energy to their world, that also affected the Doctor, draining his energy as well, causing him to regenerate.
Also In the episode it's said that his body was wearing thin.
Dan23