Responses

I think he said: "I grew up thinking that the woman who killed my birth mother was my real mother." So he is angry that he was deceived. He grew up thinking that the brunette was his real mother, and he knows now the brunette murdered our pink-haired heroine. It would be clearer said "The woman I grew up thinking was my real mother in fact, murdered my birth mother!"
Can someone explain the part in chapter 21, where elle says "I grew up thinking my real mother killed my birth mother " like what i don't understand. Hahahaahah