In English being au fait with something means being familiar with it or up to date with something. For example 'I spent my summers working as a lifeguard on Blackpool beach, so I'm completely au fait with the rules around safe swimming'. Au fait on its own has a different meaning. So you could say Au fait, j'aime bien ta nouvelle coupe de cheveux - By the way, I really like your new haircut. En fait is usually, although not always, used as a contradiction while another similar sounding phrase - en effet - is used to confirm something.

Source: The Local November 06, 2019 12:51 UTC