The royal couple was excited to introduce their new bundle of joy to the world.
Welcome to the world, royal baby No. 3!
Just hours after giving birth, Kate looked stunning in a red dress, cradling her precious baby boy with William by her side.
The couple welcomed their third child on Monday after Kensington Palace announced that the Duchess of Cambridge had gone into labor that morning. Kate gave birth at 11:01 a.m. local time to a healthy baby boy.
The newborn joins older brother, Prince George, 4, and sister, Princess Charlotte, 2. Princess Charlotte also made history on Monday, becoming the first female heir to the throne to supersede her younger male sibling in the line of succession.
Prince William kept busy right up until the baby's arrival, attending several events last week, including Queen Elizabeth's birthday celebration over the weekend. Kate attended her last official event in late March, going on maternity leave in April.
The next major event for the family will be Prince Harry and Meghan Markle's May 19 royal wedding. It's unknown whether Kate or the new baby will attend the highly anticipated nuptials, though William, George and Charlotte will all likely play a big part in the ceremony.
Keep up with all of ET's coverage of the Royal Wedding right here as we count down to May 19!