That was my initial reaction when I saw it from the tail end at the time but its not forked and Jerry has now said this is also most likely a Black Falcon. I've had mum put up her photos of the same bird which shows the notch with the outer tail feather: Unidentified on 16 Apr 2019
I confirmed this as it is the same bird as https://canberra.naturemapr.org/Community/Sightings/Details/4208200?Identified=true otherwise I wouldn't have been able to confirm it.