Sixth month anniversary dating
North Korea is thought to have carried out its most powerful nuclear weapon test to date hours after saying it had developed an advanced hydrogen bomb of "great destructive power".
An earthquake registering 6.3 was detected in the secretive state on Sunday 75km (45 miles) north-northwest of Kimchaek, where previous tests have been carried out.
The "Fall of Arcadia" becomes the central battle of the Time War around which "The Day of the Doctor" is centred.
The Eleventh Doctor and Clara Oswald aid the military organisation UNIT, headed by Kate Stewart, in investigating a mystery at the Undergallery, a secret vault housed at the National Gallery.
Realising that her rescuer is a Time Lord she refuses to comply, preferring to die rather than go with him.
Other appearances included a very brief glimpse of the then-upcoming Twelfth Doctor (Peter Capaldi), who would succeed Matt Smith in "The Time of the Doctor", As the episode celebrates fifty years of the programme, it references and alludes to various concepts featured throughout the show's run.
He reluctantly accepts that with all of reality threatened and the universe "on the brink", there is not much need for a doctor, and chooses a potion designed to initiate his regeneration into a hitherto unknown incarnation of the Doctor as a "warrior" (described in credits as the "War Doctor" and played by John Hurt).
"The Last Day" is filmed from the first-person perspective of a Gallifreyan soldier who has had a camera implanted in his head.
Its military said it has strengthened its monitoring and readiness while considering a variety of possible responses in collaboration with the US.
North Korea conducted two nuclear tests last year, the last nearly a year ago, on the 9 September anniversary of the nation's founding.