The infant's name, which has been subject to a flurry of bets, is likely to be announced in the next few days. But, his net worth is expected to climb up to around the same as theirs. A baby boy born on April 23 joins Prince George, four, and Princess Charlotte, two.
But before the young prince had his moment in front of the cameras, he got to meet his big brother and sister.
Quizzed on whether they had decided on a name, the duke added: 'You'll find out soon enough'.
However, what many of us missed was the protective gesture George, who turns five in July, made towards his little sister, set to celebrate her third birthday next month.
NBC News' interactive below takes a look at who's who in the monarchy and the line of succession.
News of the birth of the couple's third child was revealed on Twitter on Monday afternoon, in a statement from Kensington Palace. As in her previous pregnancies, the duchess suffered from hyperemesis gravidarum, a severe form of morning sickness.More news: Professor defends role in Cambridge Analytica data scandal
A large Union flag was raised over Buckingham Palace shortly after the announcement. The Duchess of Cambridge reportedly had a glam squad to help her.
The Royal Mint has even marked the arrival of the royal baby with a commemorative silver penny.
"The Queen has the facility to say what their title is - she'll decree that they're the Prince of Cambridge", defined Williams.
The top White House spokeswoman offered personal encouragement to William and Kate on becoming the parents of three children.
"I was really busy, but I saw the baby", she told PopSugar. "St. George himself would be very pleased if the baby's born today".