Clara, unable to watch, returns to the crack and through it, begs the Time Lords to save the Doctor, urging it's owed to him for all he has done in his lives. The Doctor prepares to die outside, when the crack appears in the night sky.
Regeneration energy flows from the crack and into the Doctor, granting him a new regeneration cycle and saving him from death.
The Doctor uses the excess energy of his regeneration to destroy the Daleks.
In the aftermath, Clara finds the Doctor, young again, in the TARDIS. He explains this rejuvenation is a 'reset' for the new regeneration cycle to begin and the changing of his form is taking a while to start up. He delivers a eulogy to his current form, and hallucinates a final farewell to
Amy Pond, the first person he met after
his last regeneration. He then removes his
bow tie, and drops it on the floor before abruptly regenerating into
the Twelfth Doctor. After exclaiming he has 'new kidneys' and complaining about their colour, the Doctor declares that the TARDIS is crashing and asks Clara if she knows how to fly it.