Prince William and Princess Kate Middleton arrived in New York on Sunday as part of their three-day official visit to the United States.

The Duke and Duchess of Cambridge flew in first class on a British Airways flight and checked in at the Carlyle Hotel, attracting both crowds and heavy security in the Big Apple. According to Carolyn Durand of ABC News, the purpose of their visit was primarily related to charity work.

"They are doing a number of things to support charities they really care about - disadvantaged 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.

William and Kate, who is expecting a second child in April, smiled at the well-wishing crowds. According to an Associated Press report, William's mother, the late Princess Diana, stayed at the Carlyle Hotel during her frequent visits to Manhattan in the 1990s.

Royal correspondent Max Foster commented in a CNN article on how the royal couple's visit caused commotion around the city, especially when Kate arrived at a children's craft group in Harlem and met with Chirlane McCray, the wife of New York City mayor Bill de Blasio. He noted that the Duchess has served as the nearest replacement of William's mother in their latest U.S. visit.

"They were very excited even to see the motorcade, and there is a real buzz around the city today," Foster said. "I think that association with Diana, who used to come to New York a lot -- the biggest star in the world -- and Kate seems to be the closest replacement they have to Diana in this day and age."

According to CNN, the couple's activities included a conservation reception with Hillary and Chelsea Clinton. Prince William paid a visit to Washington, where he met with President Barack Obama in the Oval Office.

The White House commented that the prince's visit highlighted "the special relationship" between the U.S. and Great Britain.

After meeting with the president, Prince William went to the International Corruption Hunters Alliance conference at the World Bank to discuss the issues of poaching and illegal wildlife trading. ABC News reported that his charity, United for Wildlife, has taken an active role in combating the lucrative ivory market.

CNN has reported that William will return to New York City and go with his wife to a NBA game featuring the Brooklyn Nets and Cleveland Cavaliers, where basketball royal LeBron James, also known as King James, will showcase his skills. The royal couple could also meet with music legends Beyonce and her husband Jay-Z, who are both part owners of the Brooklyn Nets.

As for Tuesday's plans, CNN reports that the royal couple will include a moment of reflection at the 9/11 memorial and a glitzy charity dinner for their alma mater, St. Andrews University, at the Metropolitan Museum of Modern Art in New York.

Their son, Prince George, stayed behind back in Britain. However, the British ambassador had high hopes that the royal couple's U.S. visit was a worthwhile one.

"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.