De Doctor Who Magazine número # 504, na seção que permite que os fãs façam as perguntas para o então showrunner Steven Moffat, ele tem isto a dizer:
FINLAY WORRALLO asks: Why did the TARDIS dislike Clara?
The TARDIS, being aware of all time simultaneously, was also aware that Clara was the precise motivator that would drive the Doctor to an extreme that was dangerous for all time and space. She knew, that although the Doctor loved her very much, she was bad for him and that the coming of the Hybrid would be the result of their association.
A partir disso, pode-se inferir que a associação do Doutor e Clara juntos formam o Híbrido. Time Lords e Humans são ambos referidos como raças guerreiras no episódio (veja o diálogo final entre Eu e o Doutor), que se encaixaria na descrição do Híbrido. Os bilhões de corações que eles quebrariam seriam presumivelmente os bilhões que morreriam se
Clara was kept from dying, her death being a fixed point, and preventing fixed points tears the universe apart (see The Wedding of River Song).