London, England (CNN) -- British Prime Minister David Cameron and his wife, Samantha, announced Tuesday the birth of their fourth child, a baby girl.
The baby was born by Caesarean section at the Royal Cornwall Hospital in Truro, southwestern England, at midday. She had been due next month.
The baby weighed 2.75 kilograms (6 pounds, 1 ounce), and both the baby and mother are "doing very well," Cameron's office at Downing Street said in a statement.
The child had been expected in September.
The Camerons already have two young children, Arthur and Nancy. Their oldest child, Ivan, was severely disabled and died last year at age 6.
Samantha Cameron was visibly pregnant during the campaign that brought her husband to power in May. She scaled back her hours as creative director at luxury brand Smythson after the election.
"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," Cameron told reporters outside the hospital after the birth.
"Samantha 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 at about 12 o'clock."
He added: "It was a bit of a shock. We're absolutely thrilled. She is an unbelievably beautiful girl and I'm a very proud dad and both baby and mum seem to be doing very well, so it's really exciting."