The two reality Tv colleagues were messing around for news show Extra's cameras when Stern started to quiz the German model about why she won't appear on his racy satellite radio show.
He suggested it might be because she doesn't want to talk about her marriage to Seal, stating, "I don't know what Heidi's afraid to talk about... The divorce with Seal? Who cares? Nobody cares about Seal. Alright, how big was Seal's penis?"
Klum responded, "You see this is the thing. I don't wanna talk about these things."
The German then asked Stern if he was having fun with her and their co-judges Melanie Brown and Howie Mandel, to which the radio and Tv personality got serious and said, "You could be more fun."