— -- New Yorkers rolled out the royal red carpet for Prince William and a 5-month-pregnant Duchess Kate as they arrived Sunday to the Carlyle Hotel to throngs of screaming fans.
The couple flew first class on a British Airways flight as they begin their three-day trip to the United States.
"They are doing a number of things to support charities they really care about — disadvantage young people, mental health, illegal wildlife trade, which is something they have worked on in the past," British Ambassador Sir Peter Westmacott told ABC News.
Kate upped the fashion stakes, wearing a burgundy Seraphine coat while William held her hand as they stepped out of the car at the Carlyle.
The couple then hit the town, attending an intimate dinner at the home of Martin Sorrell with 15 couples who are wealthy American donors to their Royal Foundation. Kate stunned in a black lace, knee-length dress accented with diamond chandelier dangling earrings.
They arrived without their son, Prince George, and have a packed itinerary. Prince William heads to Washington, D.C., today for a call with President Obama. He'll spend 20 minutes in the Oval Office with the president and then see Vice President Joe Biden.
"I hope that after a couple of days of this very intensive program, there will be a lot of happiness being shared, but I also hope that it will do a great deal of good for the United States and the United Kingdom," Westmacott said.
Prince William, 32, will also attend the International Corruption Hunters Alliance conference on preventing poaching and the illegal wildlife trade at the World Bank. His charity United for Wildlife has taken an active role in combating the lucrative ivory market.
The Duke of Cambridge later meets with Chelsea and Hillary Clinton for a conservation reception back in New York City that's co-hosted by the Clinton Foundation.
Meanwhile, Kate, 32, will stay put in New York City, heading to a Harlem at the Northside Center for Child Development with the first lady of New York City. The duchess is finally on the mend after her extreme morning sickness.
While security is tight around the royal couple, officials are confident that the preparation among British and U.S. security is sufficient.
"The planning is complicated, demanding, and the balance you have to try to strike is providing a level a security that you need without including any more than you have to and ensuring that they themselves can have something resembling a normal visit," Westmacott said.
"New Yorkers have always been incredibly welcoming to members of the Royal Family," he continued. "I think they were incredibly welcoming when Charles and Diana were here before. I think this will be no exception. There’s already a great deal excitement. This couple is hugely popular. They are doing their job wonderfully well. I think people will just be very excited to see them and hope they will enjoy their visit to the Big Apple."
Remarkably, neither William nor Kate has ever been to New York City or Washington, D.C. So like many couples who come to "The City That Never Sleeps," William and Kate will be keen to explore everything the city has to offer even though this is a working visit.
William will make a pit stop to take in the sights from the observation deck of the Empire State Building, while the hottest ticket in town is a fundraiser at the Metropolitan Museum of Art for the 600th anniversary of the University St. Andrews, the couples' alma mater and where they met.
The couple previously visited the U.S. after their wedding in 2011 during a short trip to Los Angeles.
"There will be so much that I’d like to show them but with a bit of luck both visits will go so well that both will want to come back regularly," said Westmacott.
After a busy day, Will and Kate head to Brooklyn for some hoops and a taste of American royalty, watching LeBron James and the Cleveland Cavaliers play the Brooklyn Nets. The couples' Royal Foundation, which supports the Coach Core program for young people, has entered into a partnership with the NBA.
The duke and duchess will attend a dinner, and then sit court-side for the second half, perhaps accompanied by a visit from rapper Jay-Z, who once owned a small stake in the Nets, and his wife Beyoncé.