After keeping the world and her mother waiting, when she finally decided to make her grand entrance, the new Princess didn't waste any time.
The Duchess, who was expected to give birth on 24 April, was a week over her due date. On the morning of 2 May, the heavily pregnant Princess finally left Kensington Palace at 6am in the early stages of labour and headed for the Lindo wing of St Mary's hospital.
Just over two hours later and the new Princess was born. The royal family's newest member was born at 8.34am, weighing 8lb 3oz. An official announcement about the birth came just after 11.15am after the couple had informed their respective families.
It stated: "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 royal couple emerged from St Mary's Hospital in London the cheering of the crowd. They smiled and briefly waved to the crowds and the world's media, as the Princess made her first public appearance.
Kate cradled the newborn in her arms. The baby was wrapped in a white shawl and a cream woollen hood.
The new mother looked radiant and relaxed in a white and yellow floral Jenny Packham dress, with a buttercup print.
The appearance lasted just a few minutes. The couple made no comment on the birth of their daughter, unlike when Prince George, the next in line to the thrown was born, at the same hospital, just 21 months ago.
Breaking with tradition and in a sign of the times, the birth was announced on Twitter.
The formal notice of birth was also placed in the forecourt of Buckingham Palace on a ceremonial easel announcing that the Princess had given birth to a daughter. Royal watchers flocked to the palace to share in a moment of history.
The brief notice confirmed the news that the Duchess of Cambridge "was safely delivered of a daughter". Presented on palace-headed foolscap-sized paper, the framed bulletin also stated that the little Princess had come into the world at 8.34am, weighing 8lbs, 3oz.
Earlier, Prince George arrived to meet his new sister. Wearing a smart blue jumper, coordinated with his father, the toddler waved somewhat nervously at the sea of photographers camped outside the hospital.
It was the first time George has been officially seen in public in the UK since he left the same hospital himself as a newborn nearly two years ago.
Carried in by his father, he was comforted with a reassuring kiss as he headed into the hospital to meet his baby sister.
Speaking to reporters briefly Prince William, who was present at his daughter's birth, said he was "very happy".
Meanwhile, the Queen was in Yorkshire on a royal military parade when the announcement of the birth of was made. Dressed in pink for a girl, the delighted great grandmother beamed broadly as she was congratulated on the royal birth. The Princess is the Queen's fifth great-grandchild
The Duke and Duchess left the hospital at 6pm in a large Range Rover driven by the new Dad.
After the months of waiting, within 12 hours, the Princess was born and was at her family home Kensington Palace.
After the excitement of the day, her older brother Prince George was taken back to the palace separately, reportedly to have a bath.
Messages of congratulations have been pouring in from around the world for the royal couple.
The Queen, Duke of Edinburgh, Prince of Wales, Duchess of Cornwall and the baby's uncle Prince Harry, the Prince of Wales and the Duchess of Cornwall all expressed their joy at the news.
The Prime Minister David Cameron, Nick Clegg and Ed Miliband conveyed their best wishes, while the US President and his wife Michelle wished the couple "joy and happiness."
The princess's name will be announced in the coming days, with reports she could be christened before the Queen goes to Balmoral for the summer in a couple of months' time.
Possible choices of name include Alice which was the name of one of Queen Victoria's daughters and f the Duke of Edinburgh's mother; Charlotte - the feminine form of Charles and Elizabeth in honour of the baby's great-grandmother the Queen. In a nod to history she may be named Victoria in honour of the baby's great-great-great-great-great-grandmother Queen Victoria. Royal watchers have speculated that the new Princess may be given a middle name of Diana in tribute to Prince William's late mother, Princess Diana.
The Princess is the highest ranking female in line to the throne, following the Prince of Wales, the Duke of Cambridge and Prince George. It's the first time a girl has been born so high up the line of succession for nearly 65 years.