Also to know is, does Kallen know about zero requiem?
Apart from Lelouch, Suzaku and C.C., only a few characters knew about the Zero Requiem before the plan was executed. So we can safely say that they did learn about the Zero Requiem at the end of the second season. Kallen and Tohdoh realize Lelouch's ultimate plan.
Subsequently, question is, does Nunnally know Suzaku is zero? Nunnally began you feel like something was not right and she then eventually realized that lelouch was zero. She has no idea who Zero is because she never gets to touch him. She did know Suzaku was hiding something from her, and she kept trying to touch him to find out but he never lets her.
Also to know, who know Lelouch was zero?
Aside from Lelouch, Suzaku and C.C., several other key characters knew about Zero Requiem, including Jeremiah Gottwald, Lloyd Asplund, Cécile Croomy, Sayoko Shinozaki and Nina Einstein, while others such as Nunnally, Kallen, Ohgi and Kaguya only realized it during and after his execution.
Who kills Lelouch?
Suzaku
