During the interval, in the mezzanine bar, drinks were served and the Queen and her husband did what they had done countless times before: they worked the room. He took one end, she took the other, and, for half an hour, the royal couple mingled, shaking hands with smiling strangers, nodding, chatting, then moving on. I stood at the edge of the crowd, watching Her Majesty and His Royal Highness as they went about their business. What they were doing, they did well. Not surprisingly. They had had a lifetime of practice. To a seasoned royal-watcher, the scene was entirely predictable. And then came the moment that took me by surprise. I witnessed it quite by chance. I happened to be looking in the right direction, that’s all, when I saw Philip catch Elizabeth’s eye across the crowded room. He simply smiled at her and gently raised his glass. She smiled back and, almost imperceptibly, raised hers. And the moment was over. But in that moment I sensed that I was seeing something I had not known about before. These two were allies engaged in a mutual conspiracy that sustained them over more than seventy years.