He didn't kill her father, he lied about killing him because he wanted to see her reaction. In his mind, she was an emotionless, power hungry bitch (extra confirmed after he witnessed her laughing like a maniac then working normally a few hours after her miscarriage lol), so when the father told him that he planned to take his daughter away, he thought "There's no way that woman would give up being queen." So he lied about killing the father, expecting her to not react much. When she tried to kill him, he was honestly shocked, but since there was plenty of witnesses and he hated her, he ordered her execution. Her dad killed himself after hearing about her execution.