Fiancé tells me shut the f up

In front of my children! It all started because he wasn’t being nice to my child and I stood up for him. Well my fiancé didn’t like that so much. So he yelled “shut the fuck up” in front of my kids to me.

I said calmly don’t you ever speak to me that way in front of my children especially! My blood is boiling! Like is this normal behavior? He never used to speak to me like this and within the last couple months this isn’t the first time I’ve heard this.