Queen who

One night at my parents' house, a few months ago, we were all having dinner - a family affair. Conversation had got onto the Royal family, not just ours either but other Kings and Queens. Cathy, who was quite a keen Royal-watcher once, hadn't been listening to our end of the table, but pricked up her ears at the sound of "queen". Queen who? she asked earnestly, and I started laughing. Mum told her but I couldn't stop laughing. I kept laughing, and my laughing went quiet and tears came out of my eyes, and everyone looked at me and smiled, and laughed a bit, but I kept on going. Eventually I caught my breath, and wiped my eyes. Queen who? I quoted, and started laughing again. I still laugh about it. Queen who?