The Duchess of Cambridge safely delivered a daughter at 8.34am today, Kensington Palace said.
Kate and the couple's daughter are both doing well. William 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, the palace added.
Kate was a number of days overdue and had been taken to the Lindo wing of St Mary’s Hospital at 6am from her nearby home Kensington Palace.
Her Royal Highness The Duchess of Cambridge was safely delivered of a daughter at 8.34am.
— The Prince and Princess of Wales (@KensingtonRoyal) May 2, 2015
Kensington Palace said in a statement: “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 Duchess of Cambridge’s daughter is fourth in line to the throne, the Queen’s fifth great-grandchild and a spare to the heir – and Prince George’s sister.
The Prince of Wales will be overjoyed as he made no secret he wanted his second grandchild to be a girl.
Before the birth William and Kate said they did not know the sex of their baby.