She didn't disappoint. The Duchess dazzled at the Metropolitan Museum of Art event, where tickets had cost guests up to £6,400 each, wearing one of her favourite gowns – a blue Jenny Packham silk dress, which was making its third outing in just over a year.
The cut of the dress gave onlookers their clearest glimpse of her growing baby bump, which until now has been kept under wraps in looser-fitting garments.
The 32-year-old accessorised with diamond and emerald earrings, with her famous locks swept up – and clearly won the approval of the cheering crowd of New Yorkers..
Among the 450 guests waiting to greet the couple was Princess Eugenie, who now lives in New York, Oliver Sarkozy and his girlfriend Mary-Kate Olsen, and Vogue editor Anna Wintour. Tom Hanks – whose daughter went to St Andrews – had been scheduled to propose a toast at the event, but had to pull out for personal reasons, and was replaced by comedian and talk show host Seth Meyers.
William, who is the patron of the 600th anniversary fund-raising campaign, spoke fondly of his time at university. "I don't need to tell all of you just how much St Andrews means to me and Catherine," he said.
Turning to Principal Louise Richardson, he continued, "It goes without saying to those in the room that the education we received there was first class. Louise, you may need to close your ears at this point but it's often said by the undergraduates of St Andrews that you leave the university in either one of two states: either married or an alcoholic.
"Fortunately for Catherine and me we ended up married. But for those of you who are parents of undergraduates right now, I give you one tip: ask your son or daughter over the holidays if they know what Ma Bells is. If they answer yes, perhaps remove their wine glasses out of reach."
The royal was referring to the bistro pub which is popular among St Andrews undergraduates.
He later added, "For Catherine and me, it will always be a very special place and we have the warmest memories of our time there as undergraduates and the friends we made there."
The evening included a dinner, held in the Temple of Dendur. Guests dined on starters of potato and leek soup, smoked haddock fishcake and Scotch lamb pie, followed by a mushroom-crusted tenderloin of Angus beef and Scottish salmon.
Earlier in the day, the Duchess opted not to join her husband on an official visit to the Empire State Building, choosing instead to rest before the dinner, and the long flight home to be reunited with their son Prince George.