What’s The Politest Way To Say, “None Of Your Business”?

I haven’t spoken to my father or his family in years. The reason isn’t really important; it’s just important to know that I don’t speak to them, don’t know where they are, and don’t care to know. 

I am a full-grown adult. My mom and I are invited to a friend of a friend’s house party so she can show off photos she took while traveling, and we are making small talk while waiting for the other guests to arrive.

Mom: “Hi, I’m [Mom] and this is my daughter, [My Name].” 

Hostess: “So, it’s just you and your mom?”

Me: “Pretty much, yep.”

Hostess: “Where’s your dad?”

Me: “Um… don’t really know and don’t want to. I don’t talk to him.”

Hostess: “Oh.” *To my mom* “Well, do you know where he is?”

My mom and I were both so baffled by the extreme rudeness of this comment that neither of us knew how to respond at all. We just kind of walked away.