I'm just curious the 12th (13th) Doctor regeneration was explained. Does anyone have their own theory on how the selanjutnya regeneration will be explained?

The explanation was diberikan in the most baru saja special episode, called The hari Of The Doctor (I think. All of these "...of the Doctor" titles can get me muddled). He had run out of regenerations and was dying. Clara spoke through a slit in time and luar angkasa to Gallifrey asking the other timelords to help him. They sent him spare regenerations. Most fan are assuming he's got another full set now.