The Duke and Duchess of Cambridge presented their new daughter to the world for the first time early on Saturday evening as they left hospital just 10 hours after the birth of their second child.
The new Princess of Cambridge slept soundly cradled in her mother's arms as the couple posed on the steps of the private Lindo wing at St Mary's hospital in Paddington, London.
Earlier, Prince George was the only visitor as he was taken to see his mother and be introduced to his baby sister, who was born at 8.34am, weighing 8lbs 3oz. Crowds cheered wildly as William, who had briefly returned to Kensington Palace to pick up his son, carried the infant prince up the hospital steps, with George, looking a little overawed, managing a small royal wave. The duke proclaimed the couple to be "very happy".
The duchess had been admitted to hospital in the "early stages of labour" at 6am and the duke attended the birth. Their daughter is the fourth in line to the throne and the Queen's fifth great-grandchild. She will be the first to take the title of princess for 25 years and will also be the highest ranking female in line to the throne. A girl has not been born this high up the line of succession in the UK for nearly 65 years, since Princess Anne was born.
In a statement, Kensington Palace said: "Her royal highness the Duchess of Cambridge was safely delivered of a daughter at 8.34am. The baby weighs 8lbs 3oz.
"The Duke of Cambridge was present for the birth.
"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.
"Her royal highness and her child are both doing well."
The news was made public once members of both families had been informed, at 11.09am. The duchess's labour was far shorter than for her first child – Prince George took more than 10 hours to be born.
She was believed to have been around one week overdue, but in the end the birth appeared to happen swiftly .
The birth was overseen by a medical team led by Guy Thorpe-Beeston, surgeon-gynaecologist to the royal household, who was assisted by Alan Farthing, surgeon gynaecologist to the Queen. Both medics were present at George's birth in July 2013.
There were cheers from the crowd gathered outside the hospital when the announcement was made. Some had been camping for almost two weeks in anticipation of the birth.
A bulletin, printed with the details of the delivery, was placed on an ornate gold easel erected by two footmen in the forecourt of Buckingham Palace. It said the duchess was "delivered" of a daughter and gave the time of birth.
Clarence House said the Prince of Wales and Duchess of Cornwall were "absolutely delighted". Other members of the Windsor and Middleton families were informed, including the Queen and Duke of Edinburgh, and Prince Harry, who is in Australia.
Prime minister David Cameron posted on Twitter: "Congratulations to the Duke and Duchess of Cambridge on the birth of their baby girl. I'm absolutely delighted for them.
Labour leader Ed Miliband tweeted: "Congratulations to the Duke and Duchess on the birth of their daughter. Wishing them lots of joy and happiness – and hopefully some sleep".