Prince William and his wife, Kate, have ended their trip to the United States at a black-tie dinner to raise money for St. Andrews University in Scotland where they met.
The three-day visit is the last the couple will make together before they have their second baby next year.
The Duke and Duchess of Cambridge had a jam-packed few days linked with youth development charities, meeting many celebrities and went to a basketball game.
On Monday, Prince William made a speech in America, warning about the effect illegal poaching is having on elephants and rhinos.
Continents like Africa and Asia used to be home to hundreds of thousands of rhinos and elephants.
But today, three out of five rhino species are critically endangered, and in Africa last year there were more elephants killed by poachers than were born.
Poaching on the rise
If that continues, experts are warning that they could become extinct within 20 years.
Despite tough hunting laws, poaching is on the rise as horns and tusks can sell for high prices on the illegal wildlife market.
Poachers kill around 35,000 elephants and 1,000 rhinos every year.
The Duke of Cambridge also spoke to US President Barack Obama at the White House, in Washington DC and hopes these talks will help to raise awareness around the world about how bad the situation is.
Meanwhile, Kate has been busy with public engagements in America too. She visited a children's centre in Harlem, New York where she met children and families and helped to wrap Christmas presents with volunteers.
William and Kate's visit to the east coast of America has been met by lots of excitement with huge crowds turning out to catch a glimpse of them.