David and Samantha Cameron have announced the birth of their fourth child, a girl.
The baby was not due to be born until next month, but was delivered by caesarean section at the Royal Cornwall Hospital in Truro.
The prime minister and his family are currently on holiday in the South West of England.
A Downing Street spokesperson said: "The prime minister and Mrs Cameron are delighted to announce the birth of their fourth child, a baby girl. Both the baby - who was born weighing 6lbs 1oz - and Mrs Cameron are doing very well.
"The PM and Mrs Cameron would like to thank the doctors and nurses at the hospital for their help and kindness."
Speaking about the birth of his new daughter this afternoon the prime minister said she would be given a Cornish middle name, although they had not decided on a first name yet.
"It was very exciting, we were on holiday, thought we were going to get through the holiday and then have a baby, and then it just seemed to kick off a bit quickly," he said.
"We woke up this morning and thought she was having contractions and it was all beginning to get going, so we thought we would come to the hospital just to get everything checked out, and then things sort of sped up and it all happened very very quickly and the baby popped out out at about 12 o'clock.
"They seemed to be doing fine and my job was to make the toast and the tea, things like that, but it's absolutely thrilling, really exciting and it's just lovely they are both doing so well."
the prime minister and his wife endured a family tragedy last year when their first born son Ivan, who suffered from cerebral palsy, died ages six.
The couple have two other children, six-year-old Nancy and four-year-old Arthur Elwen.
David Cameron is expected to take paternity leave to help care for his new daughter.
Tony Blair was the last prime minister to have a child while in Downing Street. His wife Cherie gave birth to son Leo in 2000.


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