Rodolphus hadn't heard the whisper, but when Bellatrix spoke, he did hear her. Regulus Black? It was... impossible, completely impossible. They would have known had he lived, his death and how had been well-known at the time. And to think, to think others had known. Narcissa. Even Rabastan?
However, Carina was mildly oblivious to it all, ignoring Rodolphus and taking Bellatrix's shock for delight. "Yes, yes," she said, bouncing happily as she wrapped her arms tightly around Bellatrix's neck. "He is, but no one but family knows, it's our secret. and even though he's your cousin, Tante Cissa said I could call her Tante and then Oncle Bastan let me call him Oncle and that makes you Tante and Oncle too! Isn't it wonderful?"