The Duchess of Cambridge has given birth to her third child.
Kate, 36, delivered the baby boy, weighing 8lbs, 7oz, at the exclusive Lindo Wing at St Mary's Hospital, Paddington, at 11.01am on St George's Day.
Her husband William, 35, was present for the birth, and both mum and baby are "doing well", Kensington Palace said in a statement this afternoon.
Family members have been informed and are "delighted" with the news.
"Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs. The baby weighs 8lbs 7oz," the palace said via Twitter.
"The Duke of Cambridge was present for the birth.
"Her Royal Highness and her child are both doing well."
(Image: Getty Images Europe)
(Image: Daily Mirror)
The statement added: "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 royal baby arrived into the world only about five hours after Kate was admitted to hospital in the "early stages of labour".
As the Duchess delivered her second son, crowds of well-wishers waited outside the maternity unit, holding banners and Union Jack flags.
After news emerged of the birth, they began cheering loudly and clapping.
The little boy, who is a younger sibling to Kate's two older children, George, four, and two-year-old Charlotte, is now fifth in line to the throne.
He is the Queen and the Duke of Edinburgh's sixth great-grandchild.
The birth of her third child - which comes as the country celebrates patriotic St George's Day - was confirmed by the palace shortly after 1pm.
It was also due to be marked with a traditional bulletin on show at Buckingham Palace, as well as a 41-gun salute in Green Park or Hyde Park.
A 62-gun salute at the Tower of London is also set to take place.
Although the wait for the baby's birth may be over, the public could be left guessing as to the youngster's name for several days.
The names given to royal babies are not usually revealed straight away.
Indeed, Kate and William took two days to announce both George and Charlotte's names, informing the Queen of their choice beforehand.
The couple had travelled by car from Kensington Palace to the Lindo Wing earlier today, as the Duchess prepared to give birth to their son.
Kensington Palace said in a statement this morning: "Her Royal Highness The Duchess of Cambridge was admitted to St Mary's Hospital, Paddington, London, earlier this morning in the early stages of labour.
"The Duchess travelled by car from Kensington Palace to the Lindo Wing at St. Mary's Hospital with The Duke of Cambridge."
Kate has been in the care of consultant obstetrician Guy Thorpe-Beeston, who is the surgeon-gynaecologist to the household, and consultant gynaecologist Alan Farthing, the Queen's surgeon-gynaecologist - part of the trusted team who delivered George and Charlotte.
Highly-trained midwives were also on hand as she gave birth, while experts were likely waiting in the wings in case of an emergency.
The new baby Prince of Cambridge is the younger brother of Prince George, four, and two-year-old Princess Charlotte.
He was born at the Lindo Wing this morning, weighing 8lb 7oz - heavier than both his siblings were after their deliveries.
Charlotte, at 8lb 3oz, weighed slightly less than George's 8lb 6oz.
However, she was still above average.
The average weight of a baby in the UK is around 7lb 7oz (3.5 kg). All of three of the Duchess of Cambridge's children have weighed more than 8lbs.
But the new prince is not the heaviest royal baby in recent years.
That title falls to Savannah Phillips - the daughter of the Queen's grandson Peter Phillips - who weighed 8lb 8oz in 2010.
George was the heaviest future king to be born in recent history. Prince William weighed 7lb 1.5oz in 1982, while Prince Charles weighed 7lb 6oz in 1948.
Prince Harry weighed 6lb 14oz in 1984.
The Queen - then Princess Elizabeth - was born by Caesarean section in her maternal grandparents' London home.
She was also third in line to the throne at the time, but her weight was not announced, as was previously the custom for royal babies.
Subsequent babies are usually bigger than first-born babies and weigh in around 138g (5oz) heavier, said.
For her previous births, the Duchess had a 23-strong team of top medics working or on stand-by from Imperial College Healthcare NHS Trust - which runs St Mary's Hospital.
Theatre staff were ready, along with a lab technician, replacement anaesthetists and paediatricians, a back-up for the consultant, and workers from a special baby care unit.
With George, she gave birth 10-and-a-half hours after being admitted to hospital. Meanwhile, Charlotte was delivered just two hours and 34 minutes after her mum arrived at the Lindo Wing.
Just like with her older children, Kate had been hoping for a natural birth and didn't know whether she was having a boy or a girl.
Overjoyed fans are now waiting for her to emerge from hospital with her latest bundle of joy, hoping to catch a glimpse of the royal child.
Some have been camped outside the maternity unit for more than two weeks.
Her Royal Highness The Duchess of Cambridge was admitted to St. Mary’s Hospital, Paddington, London earlier this morning in the early stages of labour.
The Duchess travelled by car from Kensington Palace to the Lindo Wing at St. Mary’s Hospital with The Duke of Cambridge.
(Image: Getty Images Europe)
John Loughrey, 63, who is part of a group waiting outside St Mary's Hospital, said earlier: "We are so pleased. We have been here for 15 days.
"I'm so pleased it's St George's Day.
"St George himself would be very pleased if the baby's born today."
Mr Loughrey, from Streatham, south London, said he planned to celebrate the birth with English flags and a portion of fish and chips.
"It doesn't matter if it's a boy or a girl as long as it's a healthy baby and a healthy mother," he said.
"It's very good for our country and of course Her Majesty the Queen."
Another member of his group, 82-year-old Terry Hutt, also expressed his delight after it was announced Kate had been admitted to hospital.
"It's fantastic to have another newborn baby," said Mr Hutt, who turns 83 at the end of the month and was hoping to share his birthday with the new royal.
(Image: Getty Images Europe)
(Image: Daily Mirror)
"If they were born on my birthday, I would have got a birthday cake."
Maria Scott, 46, from Newcastle, added: "I think it's going to be a boy and I think it's going to be quick."
The group were talking in front of their make-shift camp, including royal memorabilia and a Union Flag tent.
Kate's newborn son just missed arriving on the Queen's 92nd birthday which was on Saturday. His delivery also comes just days before the Duke and Duchess's seventh wedding anniversary, which is on April 29.
There had been speculation that Kate would choose to give birth at home, the norm for generations of royal mothers, after two problem-free labours.
But she eventually decided to return to the Lindo Wing to deliver her little boy.
She and William had chosen not to know the sex of their new baby – a pattern they have followed throughout all three pregnancies.
There had been other less pleasant similarities, with the Duchess once again suffering from the extreme form of morning sickness, hyperemesis gravidarum.
She undertook her last official engagement on March 22, while heavily pregnant with her third child, before going on maternity leave.
Chic in a £600 cream coat from Goat and a top from high street favourite Hobbs, the future Queen looked relaxed and glowing ahead of the birth.
Kate is due to attend the wedding of brother-in-law Prince Harry to American actress Meghan Markle in Windsor on May 19.
Kate and William's newborn prince is no longer allowed to jump ahead of his older sister Charlotte in the line of succession.
Previously, under the ancient rules of male primogeniture, royal sons took precedence over their female siblings, even leapfrogging first-born royal daughters.
But a radical shake-up of the royal succession rules removed discriminatory male bias and came into force in March 2015, affecting babies born after October 28 2011.
The Succession to the Crown Act 2013 has already affected the Duke of Gloucester's granddaughters, Senna Lewis and Lyla Gilman, whose younger brothers, born in 2012, now follow them in the line of succession.
Kate and William's third child is a prince thanks to the Queen, who stepped in ahead of Prince George's birth to ensure all William's children would become HRHs with fitting titles.
The Queen issued a Letters Patent under the Great Seal of the Realm in December 2012 when Kate was just a few months pregnant, declaring "all the children of the eldest son of the Prince of Wales should have and enjoy the style, title and attribute of Royal Highness with the titular dignity of Prince or Princess prefixed to their Christian names or with such other titles of honour".
A Letters Patent in 1917, issued by George V, limited titles within the royal family, meaning daughters born to William or Kate would not have been an HRH but Lady (forename) Mountbatten-Windsor instead and second or later-born sons would also have lacked the HRH title and become Lord (forename) Mountbatten-Windsors rather than princes.
George and Charlotte are expected to have a starring role.
Kate and William met in 2001 when they were at the University of St Andrews, in Scotland. They dated for 10 years and got engaged in Kenya in October 2010.
Their lavish wedding at Westminster Abbey in April 2011 was watched by millions around the world and revitalised a monarchy dogged by scandal and haunted by the spectre of William's mother, Diana.
Kate was young, fresh and from a family who provided the stability that both her husband and his brother Harry had lacked.
The couple's first child George Alexander Louis was born in July 2013 after a difficult pregnancy. The Duchess had suffered deeply debilitating morning sickness which had left her hospitalised.
While she was being treated, two Australian radio station presenters made a prank call pretending to be the Queen and Prince Charles.
Jacintha Saldanha, a nurse at King Edward's Hospital where Kate was being treated, believed the hoax and put them through to the ward.
She committed suicide days later.
The Cambridges' second child Charlotte Elizabeth Diana was born in May 2015.
Her name is a tribute to grandfather Prince Charles, the Queen, Kate's great-grandmother (also Elizabeth) and William's mother, the late Princess of Wales.
It is understood Kate was taken to the Lindo Wing before 6am today for the birth of her and William's third child.
The new arrival's home will be a lavish 22-room apartment at Kensington Palace which was extensively refurbished to the couple's specifications.
Kate's third child - and second son - was born on St George's Day. The patron saint of England, St George is heralded for his honour, bravery and gallantry.
Surrounded by myth, one legend tells of St George's defeat of a dragon.
The actual St George was born in Cappadocia - an area now in Turkey. He lived during the 3rd century, becoming a Roman soldier.
He protested against Rome's treatment of Christians, and was imprisoned and eventually executed for refusing to denounce his faith.
The flag of Saint George - a red cross on a white background - is the flag of England and is incorporated into the Union Jack.
The royal baby also shares his birthday with Lady Gabriella Windsor - the daughter of Prince and Princess Michael of Kent, who was born at the Lindo Wing, where Kate gave birth, on April 23, 1981.
The latest addition to the Cambridge family is fifth in line to the throne, with Prince Harry now shifted down the line of succession to sixth place.
The Duke of York, who was born second in line, has moved to seventh, while Princesses Beatrice and Eugenie are now at eighth and ninth.
It was always thought that William and Kate would go on to have three children.
Kate, one of three, had a happy home life with her sister, Pippa Matthews, and brother, James Middleton, and is close to both of her siblings.
But William may need to adjust to caring for a newborn once again.
(Image: Getty Images Europe)
Kate joked in the months leading up to her due date that her husband was "in denial" about having a third.
By having more than two children, the couple have followed in the footsteps of the Queen and the Duke of Edinburgh, who went on to have four kids.
As a sibling to both future king George and "spare to the heir" Charlotte, the new baby boy is unlikely ever to be crowned sovereign.
However, although it is rare, it is not unheard of for a third-born royal who is in direct succession to become monarch.
William IV, who who ruled from 1830 to 1837, was a third child and acceded to the throne when he outlived his older brothers.
The Lindo Wing, where Kate has given birth to all three of her children, is a private facility offering "world-class maternity care".
The Duke of Cambridge and Prince Harry were also born at the exclusive unit.
It boasts en-suite rooms "providing a modern, homely environment in which to start your new or expanded family life", according to the unit's website.
Deluxe rooms and suites are also available.
The latest price list, from July last year to March, states that a standard room package, including a one-night stay, costs from £5,900, while a deluxe package is £6,275 - with an extra night priced at more than £1,000 for both options.
The price of a suite of two rooms, with one used as a living room, is available on application but five years ago it cost £6,265 for a one-night stay.
With standard and deluxe care packages rising by around £1,000 since the birth of their first child, William and Kate could have spent close to £7,500 for a suite, with consultants' fees on top of this.
Each room has a satellite TV with major international channels, radio, bedside phone, fridge, free wi-fi and a choice of daily newspapers.
All meals are freshly prepared in a dedicated kitchen and there is even an afternoon tea service, for parents to celebrate their new arrival.
The Lindo Wing's internationally renowned obstetric unit caters for complex pregnancies and deliveries, as well as multiple births.
It has the benefit of being based in an NHS hospital if further complications arise, including its facilities for premature babies in the Winnicott Baby Unit.
In 2006, William visited the refurbished NHS neonatal unit at St Mary's, cradling two tiny premature babies - one weighing just 5lb.
Diana, Princess of Wales visited St Mary's in April 1997, when she toured the paediatric intensive care unit, meeting poorly youngsters.
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