Why did my dog randomly attack my cat?

I have a four year old dog and an 11 year old cat. My dog has known my cat her whole life. They’ve always gotten along and are usually very affectionate towards each other. We were all in my living room when my dog randomly attacked my cat. This wasn’t a playful attitude either, she was genuinely trying to hurt my cat. I’ve never seen my dog act like this in general, not to other people or other animals. I have to physically pull her away from my cat and crate her up. Does anyone know what might have caused this? I’m genuinely shocked by the whole situation.