Royal baby: Quicker birth time second time round for Kate Middleton
Kate Middleton gave birth just two hours and 34 minutes after being admitted to hospital.
The speedy announcement came after a lengthy wait for news of developments over the last week.
It appeared to be a much faster delivery than with Prince George - although Kate could have been in labour at home for several hours before she was admitted.
In 2013, she went into hospital at around 6am on the day George was born and he arrived 10-and-a-half hours later at 4.24pm, weighing 8lb 6oz.
Second and subsequent labours tend to be much faster, with active labour lasting, on average, five hours, according to parenting site BabyCentre.co.uk.
Mervi Jokinen, of the Royal College of Midwives and president of the European Midwives Association, said: "Individual labours are different, but we definitely see shorter labours second time around.
"Your body seems to be programmed. The hormones kick in quicker and progression is faster. It's a little bit like a computer. Your body needs to be programmed first time around.
"The pushing stage can also be quicker because it's your second one. Muscles have been stretched so you have less resistance and you have the ability to push the baby past the birth canal."
Kate had a straightforward birth with George with no complications and, given the quick confirmation of the birth from Kensington Palace, is likely to have had the same this time.
As well as having a hospital bag packed with nappies and babygros, Kate will have made preparations for leaving the Lindo Wing in front of the world's media.
Her hairstylist Amanda Cook Turner has reportedly gone into the Lindo Wing around 2pm today - prompting speculation Kate will leave the maternity hospital later this evening.
Ms Cook was reportedly put on notice for the birth a month ago.
For George's birth, the hairdresser was called to the Lindo Wing, along with Kate's assistant Natasha Archer, who carried a selection of dresses, to help style her ahead of her appearance with her day-old baby son.
Sasha Miller, managing editor of parenting site BabyCentre.co.uk, said second labours are usually easier as well as quicker.
"You know what you're doing and you don't have the anxiety of last time," she said.
Second-time mothers also often leave hospital much quicker as well - sometimes as soon as four to six hours after the birth - so they can be reunited with their first child.
"With your first baby, the midwives encourage you to stay to make sure you're okay and help you breastfeed. But with your second you're much more confident. Mums also want to get home to see their first-born," Ms Miller said.
She urged Kate to make sure she allows herself time to recover from the birth.
"With your second child, you don't have the luxury of devoting time to just yourself and your new-born. Kate does have help at home but she still has that emotional pull towards spending time with George," Ms Miller said.
"Although you might be up and about quicker with your second, you have to take time for your body to recover."