(it's) news to (one)
This is something I was not aware about or did not know. A: "Yeah, Jeff and Anthony have been going out for a few months now." B: "It's news to me. I thought they were just friends." We're not allowed to dump grass clippings here? Hmm, news to me!
it’s/that’s ˌnews to ˈme
used to express surprise at some information that you have just heard: ‘Max is thinking of leaving his job.’ ‘Really? That’s news to me. I thought he was happy there.’