Male cat bitting spayed female cat and bitting fur off neck

Hello, I have an aggressive alpha male cat who is biting the fur, in patches, off the back of a black in color spayed females neck. The aggressive male is neutered too. The male thinks the black female cat is another black male cat that comes around on occasion and misdirects his aggression at her. He has bitten 4 patches of fur of the back of her neck, the worst this morning. The female is a very sweet 3 year old feral cat that has been around my home all her life. She keeps to herself and I have just started petting her within last 6 months. My question is, how to stop the aggressive male from his destructive behavior. The aggressive male cat has been around as long as the female, but did not start this behavior until as of late. He did not start this behavior until soon after he became neutered. The other black male cat has been around the yard for over a year now, and the aggressive alpha male has pretty much just left him alone for the most part but has now started this misdirected destructive behavior at the black female cat. I understand why, I just want to stop this destructive behavior against the black female and I am not always around. Help!!! Thank You.