should I tell him I'm having his baby?

Ok to make a long story short, I'm 21 weeks pregnant with my ex-fwb I guess we'll call him (we were each others booty call I guess) at first I didn't know who was the father of my son but I've gotten it all figured out now and I don't know when to tell him or how to tell him or even if I should tell him? I've moved to a different country and only recently found out I'm pregnant he has a girlfriend now. It's going to be hard to prove that my son is his since we live far away but ideally I'd like to give him rights to  our child? What do I say?