Ex Allows His Fiancé To Swear At Our Kids

I have a question for any of you ladies who has an ex who allows their new interest, girlfriend, fiancé, or wife to yell and swear at their kids. My ex’s fiancé was yelling at my daughter yesterday and she called her an asshole loud enough to be heard throughout the neighborhood. My ex didn’t even call his fiancé out on it and just let her do what she will. It’s like the man literally handed his balls over to someone he’s been with for barely a year. Hell, she already had them firmly in hand by their third month of dating. Anyway, my daughter said she couldn’t tell me too much about what happened or her dad and his fiancé would get really pissed at her for telling me. My question is, should I let the fiancé get away with calling my daughter that and should I call my ex out for allowing it? I need some suggestions on the vest way to handle this. Frankly, I’m about to lose my shit on both of the “adults” in their house.