He didn’t kill Tutankhamun – at least that is the conclusion of a study of the mummy. It rejected a conclusion from a 1960s study that Tut died from a blow to a head (for which his successor was a natural suspect), blaming the damage their on excavators.
Instead, it finds a severe broken leg and open wound that probably would have resulted in death from scepticaemia or similar.
So it may have been the horse that did it…