Crown prince of Dubai Sheikh Hamdan bin Mohammed bin Rashid al Maktoum partook in Serendipity 3’s Golden Opulence Sundae in royal fashion Saturday night. His royal highness arrived at the Upper East Side eatery, spies said, with an eight-person posse of bodyguards, plus women “all in black,” to savor the $1,000 dish (which comes complete with edible gold and Tahitian vanilla ice cream). The sundae is served in a $300 Baccarat goblet. And when the Dubai royal received the receptacle in a red velvet-lined box at the end of his meal, he quipped, “I would have ordered one for each person if I knew I got to keep the glass!” Sources told us the prince paid his bill in cash and left the waiter a generous tip.