HOT News: Kate is expecting the fourth child! Prince William shared the joyous news following his wife’s successful cancer treatment: “We are excited to announce the arrival of our fourth royal baby…”

Princess Kate and Prince William are celebrating the birth of a bouncing baby girl.

The little one, a sister for their 21-month-old son Prince George, was born at St. Mary’s Hospital in London – just hours after Kate arrived at the private Lindo Wing.

The baby weighed in at a healthy 8 lbs., 3oz. In a royal first, Kensington Palace broke the news on Twitter, saying: “Her Royal Highness, The Duchess of Cambridge was safely delivered of a daughter at 8.34 a.m. Her Royal Highness and her child are both doing well.”

Cheers of “God Save the Queen” rang out from crowds of well wishers waiting outside minutes after the birth was announced.

While the baby’s name will be revealed “in due course,” the palace said, she will be given the title Her Royal Highness, Princess of Cambridge.

Prince William was by Kate’s side as she was whisked to hospital just before dawn at 6 a.m. – and was present at the birth, it was confirmed.

News of the birth was announced in a statement by Kensington Palace at 11 a.m. in London, followed by a flurry of Tweets on its official Twitter account two minutes later.

“The Queen, the Duke of Edinburgh, The Prince of Wales, the Duchess of Cornwall, Prince Harry and members of both families have been informed and are delighted with the news,” the palace said.

Although Kate was overdue, in the end her labor went quickly, and a source told PEOPLE that she caught everyone by surprise.

The birth was believed to be natural, as the source said: “That was the plan.”

The same medical team who delivered Prince George at the very same hospital on July 22, 2013, delivered his sister.

The princess is the fourth in line of succession after Prince Charles, Prince William and Prince George.

 

The team in charge of Kate’s delivery was Mr. Guy Thorpe-Beeston, Surgeon Gynecologist to The Royal Household, Mr. Alan Farthing, Surgeon Gynecologist to HM The Queen, Dr. Sunit Godambe, Consultant Neonatologist at Imperial College NHS Trust, Professor Huw Thomas, Physician to HM The Queen and Head of the Medical Household.

William, 32, and Kate, 33, left George with nanny Maria Borrallo and arrived at the Lindo Wing of St. Mary’s hospital in London on Saturday morning at 6 a.m. after Kate went into labor.

Per royal protocol, an official announcement will be posted with the full details on an easel in the forecourt of Buckingham Palace – just as happened when Prince George was born on July 22, 2013.

It’s expected that close relatives – led by Kate’s parents, Carole and Mike Middleton, and William’s father Prince Charles and his wife, Camilla, Duchess of Cornwall – will come to see the couple and their as-yet-unnamed newborn before the young family leaves the hospital.

 

Following the celebratory formalities, including a gun salute in one of the London parks, the couple is expected to take their baby home to nearby Kensington Palace, where reigning monarch (and great-grandma) Queen Elizabeth may then visit.

As the couple takes in their first moments with the new baby, royal fans have gathered outside the hospital in hopes of another mini press conference like the one William and Kate held to debut George.

The birth follows weeks of building royal baby fever, as bookmakers ran races of royal favorite corgis to guess the baby’s gender while fans wagered on possible names.