My feeling has always been that if I’m going to get engaged, then the number of people who know that before I do should be either 0 or 1. People here are talking about it being a “respect” thing to ask for the dad’s blessing (but don’t worry, not permission, just support!), but to me it seems hugely disrespectful to the proposee. I get that everyone is different and some people don’t mind it, or even prefer it - I just want to stress the importance of making sure someone is on the same page as their SO before doing this, because it is by no means guaranteed that that’s what someone wants.

100% agreed. I know men who have done this, and I know women who have been ok with it, but if my husband had done anything like this, we would not be married. OP, please make sure this is something your gf is ok with before doing it.