Son's holiday project is a family tree, and he's asking about the uncle nobody mentions

Class 7 holiday homework: a family tree going back three generations, with a photo and one line about each person. He's spent two days on the phone with his grandmother and is enjoying it far more than I expected. Then he asked why one of my partner's brothers isn't in a single photo. There was a falling out before he was born. Nothing dramatic, just years of not speaking, and now nobody quite remembers how to start again. Do I give him the short version, leave a blank box, or send him to my partner? He's 12. He will notice a blank box.