Looping back, I just had a thought… Doesn’t the existence of “Bi-generation” where a Time Lord can split into two entities create a strong case for the origin of The Valeyard? What if Doc 10 bi-generates again, and out comes The Valeyard? He was described as “somewhere between your 12th and final incarnation” back when 13 was the natural number of lives. With The War Doctor, we knew Tennant to actually be 11, but then he also did a weird half regeneration thing as well, didn’t he? That would put his number at 12. And now he is back. Primed to perhaps become The Valeyard as some part of him inside becomes dissatisfied with the domestic life he’s now chosen.