The new prince is fifth in the line of succession to the throne.
On Monday, April 23, Kate Middleton, the Duchess of Cambridge, gave birth to a son, weighing 8 pounds, 7 ounces.
The announcement was posted on the official Kensington Palace Twitter account, which noted that Prince William was on-site for the birth of the couple's third child. The new baby will join siblings Prince George and Princess Charlotte, who are 4 and 2 years old, respectively.
As is tradition, a birth notice was posted in the court in front of the palace, where it'll stay for 24 hours before being sent to the Privy Council Office for official recording.