Why did Musa say to his brother Harun, "O son of my mother, seize not my beard," and not "O son of my father"? And why did he address him by kinship to their mother and not their father?

The exegetes mentioned that Harun's call to Musa, "O son of my mother," was for supplication and seeking mercy. It was also said because she was a believer, and it was also said because he was his brother from his mother only, not his father. Al-Qurtubi said: It was a word of tenderness and affection. Al-Zajjaj said: It was said that Harun was Musa's brother from his mother, not his father.