This question already has an answer here:
At the start of season 6, we see the Eleventh Doctor being shot midway through his regeneration, in order to kill him.
However, we now know that this incarnation of the Doctor was the last Doctor of this cycle (the “thirteenth” regeneration), and he didn’t have a new set yet. So the Doctor couldn’t be regenerating; one shot would have killed him instantly, rather than causing him start to regenerating.
How can we reconcile these two events?