The royal baby was born at St. Mary’s Hospital at the private Lindo Wing in London, England and weighed in at 8lbs 7oz.
Prince William was present for his son's birth, and both the baby boy and Kate are doing well.
The Duke and Duchess of Cambridge's newborn, whose name has not yet been announced, joins 4-year-old brother Prince George and sister Princess Charlotte, who turns 3 in May.
The new royal baby is fifth in line to the throne after Prince Charles, William, George and Charlotte.
Prince Harry, who was fifth in line, has been bumped to sixth place.
William and Kate first announced that the couple were expecting their third child in September 2017.
The Duchess of Cambridge went into labour on April 23, Kensington Palace confirmed.
Like her first two pregnancies, Kate suffered from Hyperemesis Gravidarum, an extreme form of morning sickness during her third pregnancy with the newborn royal.