I'm going to stick my nose where it doesn't belong.
Why do you want to be so nosy?
It's because his mother is my father's old girlfriend, and I need to tell him about it.
Well I think that you should not do that. It is rude to get involved in other's problems. They have nothing to do with you.
You don't know what you're talking about.
I'm not an expert, but I'm sure that getting involved in someone else's personal relationship is not the right thing to do. I think you should just leave it alone, and wish them the best.