The new parents came down the steps outside St. Mary's Hospital's private Lindo Wing with Kate cradling the future monarch in her arms. The two posed for photos and briefly answered a few questions posed by the media.
It's the same stairs that Princess Diana introduced William to the world 31 years ago.
A smiling Kate, who wore a pale blue polka-dot dress, said she felt "very emotional." She passed the baby to her husband, who appeared relaxed and joked with reporters.
"He's got her looks, thankfully," William said. "He's got a good pair of lungs on him, that's for sure."
William added: "He's a big boy, he's quite heavy," and laughed when a reporter asked him about the baby's hair.
"He's got way more than me, thank God," he said. He also said they're still working on a name.
The couple re-entered the hospital to place the child in a car seat before re-emerging to get into an SUV. William drove the couple away - palace officials said they headed to an apartment in Kensington Palace from the hospital.
Tuesday morning, Kate's parents, Mike and Carole Middleton, arrived at the hospital to visit. But Monday night, it was just the three of them. The palace said Tuesday that "mother, son and father are all doing well this morning."
The baby was born weighing 8 pounds 6 ounces at 4:24 p.m. London time. The official birth announcement didn't come until nearly four hours after the birth, so that the couple could call family and friends to personally share their news.
While the couple did keep with tradition by having the birth announcement displayed outside Buckingham Palace, that came after they announced the birth in an email.
Officials say William was with Kate throughout the entire birth and also stayed with her at the hospital overnight, which is also rare for a royal.
The couple will raise their bundle of joy in apartment 1A of Kensington Palace, which has more than 20 rooms. It's also the same palace in which William grew up, noted for its ornate interior décor and picturesque gardens.
In a statement, the new parents said, "We would like to thank the staff at the Lindo Wing and the whole hospital for the tremendous care the three of us have received. We know it has been a very busy period for the hospital and we would like to thank everyone - staff, patients and visitors - for their understanding during this time."
Lots of celebrations were scheduled Tuesday, including gun salutes by royal artillery companies to honor the birth and the ringing of bells at London's Westminster Abbey.
News of the royal baby also set off celebrations in Southern California. Local newsstands in Studio City were brimming with headlines marking the new prince's arrival. Many Southlanders celebrated in British Pubs and restaurants. Patrons toasted champagne and even had high tea to rejoice the birth of the royal couple's first child.
Canada found a special way to announce the royal birth. Niagara Falls was illuminated with blue lights, to signify the birth of the future king.
The Associated Press and ABC News contributed to this report.