Kate Middleton has been admitted to hospital in the early stages of labour.
The Duchess of Cambridge was taken by car to St Mary’s Hospital ahead of the royal birth at 6am on Saturday.
Prince William was at her side as she was admitted to the Lindo Wing, where it has been confirmed by Kensington Palace, her 'labour is progressing as normal'.
Kensington Palace released a statement via email to the press which was then followed two minutes later by a tweet confirming the admittance.
Officials have said the duchess and the prince do not know the sex of their unborn child.
The Lindo Wing at St Mary's Hospital in west London is where her first child, Prince George, was born in July 2013.
Both Prince William and his brother Prince Harry were also born at the Lindo Wing.
The new baby will be fourth in line to the throne, behind his or her grandfather Prince Charles , father Prince William and brother Prince George.
On Thursday, during an official engagement, Prince Charles said he was hoping the duchess gave birth to a girl.
Catherine, who is thought to be overdue, is being looked after by consultant obstetrician Guy Thorpe-Beeston.
He will be joined in the delivery room by Alan Farthing, the Queen's surgeon-gynaecologist.
Catherine went on maternity leave on March 27 when she carried out her last official public engagements before the birth.
Fans of the Royal Family have been camping outside the hospital with flags and banners over the last two weeks.
However in an effort not to repeat scenes at the time of Prince George's birth, the world's press were stopped from camping outside in advance.
The birth will be announced in an email to the press. Two minutes later, a tweet will be posted on the Kensington Palace Twitter feed - @KensingtonRoyal .
There will also be the traditional custom of placing a paper announcement outside Buckingham Palace.