She checked into the hospital in early labor around 6 a.m. London time.
She gave birth at 11:01 a.m.
By around 6 p.m., she was standing on the steps outside St. Mary's Hospital in Paddington cradling in her arms the newest member of the British royal family — a possible King of England.
Just seven hours after giving birth to His Royal Highness, she was back home at Kensington Palace.
The Duchess of Cambridge makes birthing babies look so easy.
"Kate Middleton pops out babies so quick, like ... Eggo waffles," snarked one Twitter user.
She actually tarried a bit on this, her third delivery and her biggest baby yet at 8 pounds, 7 ounces.
Kate's second baby, Princess Charlotte, came quicker, born on the morning of May 2, 2015, just two and a half hours after Kate was admitted to the hospital, according to The Daily Mail. Kate was in the hospital for just 10 hours with her only daughter.
Kate stayed in the hospital for more than 24 hours when she gave birth after more than 10 hours of labor to her first child, George, on July 22, 2013.
In-and-out deliveries are not unusual in the United Kingdom, where British mothers are sent home from the hospital after childbirth more quickly than in any other developed country, British researchers found in a study two years ago.
In the United States, new moms are said to spend an average two days in the hospital with their newborns. In the U.K., new moms stay an average day-and-a-half.
“The length of time a woman spends in hospital will vary depending on their needs,” Louise Silverton, director for Midwifery at the Royal College of Midwives in London, told Britain's The Guardian in 2016.
“Midwives need to check to make sure women feel up to going home. However, provided the woman is medically fine, has the support she needs at home and the right postnatal care plan in place, and a good community midwife service, then going home even five or six hours after birth may be absolutely fine.”
People magazine points out another reason for Kate's quick getaways: The frenzy her presence causes at the hospital.
For all three of her births, media and fans camped for days outside the hospital's private Lindo Wing — where William's parents, Princess Diana and Prince Charles, posed with him and his brother, Harry, when they were born.
People magazine also noted that Kate's red dress seemed to be a nod to the red ensemble the late Princess Diana wore when she presented Prince Harry to the public.
Women were awed at the job her hair and makeup team did on the new mom — again.
The media scrum and accompanying noise can be disruptive for other mums having babies there. And, unlike non-royal mums, Kate has a medical team at her disposal once she gets home.
Kate's stay was so short that no one else from the family, other than George and Charlotte, visited. Charlotte managed to steal the show by waving to the crowds. The Daily Mail reports that the rest of the family will meet the baby at Kensington Palace on Tuesday.
William and Kate didn't know they were having a boy; they reportedly wanted to wait to find out the baby's gender.
The new prince was born on William Shakespeare's birthday.
If the past is any predictor, his name won't be announced for a couple of days, but people have already placed their bets. Literally.
Current favorites with British bookies: Arthur, Albert and Phillip.
The BBC reports there's a slight chance the new little prince will be named after someone from the mom's side of the family.
The most popular baby boy names in the United Kingdom right now are Liam, Noah, Logan and Oliver. But royal watchers say don't hold your breath for a Prince Logan.
"Tradition plays a huge part in the British Royal Family, even in the 21st century," Joe Little, managing editor of Majesty magazine, told the BBC.
"It will probably be something we have heard attributed to a prince... before. It's quite likely to follow the traditional route that William and Kate seem to favor."