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

The explanation was دیا in the most حالیہ special episode, called The دن 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 space to Gallifrey asking the other timelords to help him. They sent him spare regenerations. Most شائقین are assuming he's got another full set now.