Prince William and Duchess Catherine have named their baby son Prince Louis Arthur Charles.
The royal couple - who are already parents to Prince George, four, and two-year-old Princess Charlotte - welcomed their third child into the world on Monday and have now announced his name following days of speculation.
Kensington Palace announced in a statement: "The Duke and Duchess of Cambridge are delighted to announce that they have named their son Louis Arthur Charles.
"The baby will be known as His Royal Highness Prince Louis of Cambridge."
The youngster takes one of his names from his grandfather, Prince Charles.
News of the birth of the couple's third child was revealed on Twitter on Monday afternoon, in a statement from Kensington Palace.
It read: "Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs.
"The baby weighs 8lbs 7oz.
"The Duke of Cambridge was present for the birth.
"Her Royal Highness and her child are both doing well.
"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."
On Monday evening, 36-year-old Catherine - who also has four-year-old Prince George and two-year-old Princess Charlotte with Prince William - left St Mary's hospital in Paddington, London, and was pictured outside the ward with her 35-year-old spouse and their new arrival.
Meanwhile, Prince William thanked the medical staff who helped deliver his son.
A separate statement read: "Her Royal Highness The Duchess of Cambridge will be leaving St. Mary's Hospital this evening. The Duke and Duchess of Cambridge and their son will travel home to Kensington Palace.
"Their Royal Highnesses would like to thank all staff at the hospital for the care and treatment they have received. They would also like to thank everyone for their warm wishes."
Prince William's newborn son sleeps 'well'
Prince William has revealed his newborn son - who is yet to be named - is sleeping well and is "behaving himself."
The 35-year-old royal welcomed his third child into the world with his wife Duchess Catherine on Monday and, although it's still early days, the tiny tot is "behaving himself" thus far and isn't having his parents up too much in the night.
William joined his brother Prince Harry and his fiancee Meghan Markle at Westminster Abbey to mark Anzac Day on Wednesday (25.04.18) and said when asked how the duchess and baby were doing: "They're very well thanks.
"They are in good form, luckily. Sleeping's going reasonably well so far, so he's behaving himself which is good news."
The couple - who also have four-year-old son Prince George and two-year-old daughter Princess Charlotte together - are yet to announce the name of their baby, but William did joke that "Jerry's a strong name" after he met the New Zealand High Commissioner to the UK, Sir Jerry Mateparae at the beginning of the service.
The Dean of Westminster suggested: "Jerry would like it to be Jerry."
To which the prince replied: "Jerry's a strong name."
Prince William, Prince Harry, right, and Meghan Markle arrive to attend services commemorating Anzac Day at Westminster Abbey in London, Wednesday, April 25, 2018. ANZAC Day commemorates the moment when Australian and New Zealand Army Corps troops waded ashore at the Gallipoli peninsula in Turkey 103 years ago in their first major battle of World War I.
The duchess, 36, was taken into St. Mary's hospital in Paddington, London, in the early hours of Monday morning in labour and by 11am the prince had been born.
Shortly after the baby's birth, Kensington Palace confirmed in a statement: "Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 1101hrs.
"The baby weighs 8lbs 7oz.
"The Duke of Cambridge was present for the birth.
"Her Royal Highness and her child are both doing well."
Both William and Catherine's family are "delighted" with the new addition.
The statement concluded: "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."
Royal baby: Prince Charles welcomes new grandson
Prince Charles says it is a "great joy" to be a grandfather once again, issuing a statement to express his pleasure with the arrival of a boy to the Duke and Duchess of Cambridge.
The 8-pound, 7-ounce (3.8 kilogram) boy was born Monday morning. The new prince is fifth in line to the throne and is a younger brother to 4-year-old Prince George and Princess Charlotte, who turns 3 next week.
Charles said in a statement Tuesday that "it is a great joy to have another grandchild, the only trouble is I don't know how I am going to keep up with them."
The birth is being marked by bell ringing at Westminster Abbey and a gun salute in London's Hyde Park.
Prince charming: Kate gives birth to boy, home by suppertime
Third time's a charm. The duchess of Cambridge gave birth Monday morning to a new prince who is fifth in line to the British throne - and she was home by suppertime.
The duchess and husband Prince William drove to St. Mary's Hospital in London early in the morning, and Kate's 8 pound, 7 ounce (3.8 kilogram) boy was born at 11:01 a.m., with royal officials announcing the birth about two hours later.
There followed a smoothly choreographed operation perfected after the births of the couple's two other children. In late afternoon, elder siblings Prince George and Princess Charlotte were brought to meet their baby brother. Around 6 p.m., Kate emerged alongside her husband, wearing a vibrant red dress and holding the tiny royal highness wrapped in a white lace shawl.
After posing for dozens of photographers and camera crews outside the hospital's private Lindo Wing, the trio headed home, with the baby nestled securely in a car seat. Television news helicopters followed the royal Range Rover as it made the mile-long (1.6 kilometer) journey to the family's Kensington Palace residence.
William declared the couple "very delighted" with the new addition to the family.
The royal palace said "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." Prime Minister Theresa May offered "warmest congratulations."
News of the royal birth came with a mix of tradition and modernity typical of Britain's media-savvy royal family. It was announced on Twitter and also proclaimed in the forecourt of Buckingham Palace with a framed notice perched on a golden easel.
Tony Appleton, a town crier from southeast England, showed up in full regalia to declare the newborn prince's birth outside the hospital. The words "It's a boy" flashed in lights around the top of London's BT Tower, which can be seen for miles around.
More ceremonial celebration will come Tuesday, including the pealing of bells at Westminster Abbey and a gun salute in London's Hyde Park.
The baby is a younger brother to 4-year-old Prince George and Princess Charlotte, who turns 3 next week. Both were born at the same hospital, as were William and his younger brother, Prince Harry.
The infant's name, which has been subject to a flurry of bets, is likely to be announced in the next few days. Arthur and James are among bookmakers' favorites for the new prince, whose full title will be His Royal Highness, Prince (Name) of Cambridge.
"You'll find out soon enough," William said when asked about the baby's name.
Monday is St. George's Day, England's national day, but the baby is unlikely to be given the name since his older brother already has it.
The new arrival is Queen Elizabeth II's sixth great-grandchild and bumps Prince Harry to sixth place in the line of succession. The baby is fifth in line, after grandfather Prince Charles, father Prince William and his two siblings.
Charlotte is the first royal daughter to stay ahead of a younger brother in the line of succession. Before the rules were changed in 2012, male heirs took precedence.
Kensington Palace announced in September that Kate was pregnant with her third child. As in her previous pregnancies, the duchess suffered from hyperemesis gravidarum, a severe form of morning sickness.
Officials announced her previous pregnancies before the traditional 12-week mark because she was too unwell to attend public engagements. This time around, it kept her from taking George to his first day of school.
The 36-year-old duchess, formerly Kate Middleton, nevertheless kept up a busy schedule of royal duties during her pregnancy, including a visit with William to Scandinavia. She carried out her last official engagement on March 22 before going on maternity leave.
The birth was overseen by a team of doctors including consultant obstetrician Guy Thorpe-Beeston and consultant gynecologist Alan Farthing - who were also called in for the births of George and Charlotte - as well as the hospital's midwives.
Television crews, journalists and royal fans had set up camp outside the hospital for the "royal baby watch" since early April in anticipation of the arrival.
The top White House spokeswoman offered personal encouragement to William and Kate on becoming the parents of three children.
"From one mother to another, I know the reality of being outnumbered can be very scary, but I know she and Prince William will continue to be amazing parents," Press Secretary Sarah Huckabee Sanders, herself a mother of three, said during a White House briefing.
John Loughrey, a veteran royal-watcher who camped outside the hospital for two weeks, said the baby would be "very good for our country and of course, Her Majesty the queen."
"I'm so pleased it's St. George's Day," he said before the birth was announced. "St. George himself would be very pleased if the baby's born today."