What to say to someone who's nonna just passed away?

My friend that im getting fair close with informed me this morning that his nonna passed away last night. I'm not sure of how she died, how old she was etc, but i don't know what to say to him now in conversation. What things can i say that will comfort him? I don't know if i should you know talk to him about it so that he doesn't bottle things up but then i don't want to push him away. His only 17.