Prince William and Princess Kate have welcomed a baby boy.
Kate, 36, delivered a son in the Lindo Wing at St. Mary's Hospital, Kensington Palace announced.
The newborn, the third child of William and Kate, weighed 8 pounds, 7 ounces at birth. He was born at 11:01 a.m., local time.
William, 35, was present for the baby's birth, according to Kensington Palace.
He departed the hospital a few hours after the baby's birth was announced, and later returned with the baby's older siblings, Prince George, 4, and Princess Charlotte, who turns 3 on May 2.
William and Kate posed for the assembled media and fans outside St. Mary's Hospital with their newborn later in the day.
The couple and their third child then traveled from the hospital to their residence at Kensington Palace.
"Their Royal Highnesses would like to thank all staff at the hospital for the care and treatment they have received," Kensington Palace said in a statement. "They would also like to thank everyone for their warm wishes."
The baby is Queen Elizabeth II's sixth great-grandchild.
Early in her pregnancy, Kate suffered from hyperemesis gravidarum, or extreme morning sickness, as she did with her first two pregnancies. Kensington Palace announced Kate's pregnancy in September.
During her pregnancy, Kate maintained a busy pace of royal engagements, including a trip with William to Norway and Sweden and the launch of a mental health program in schools.
She is expected to now take time off from official royal duties, as she did after the births of her older children.
How the baby's birth is announced
Once Kate gave birth, Queen Elizabeth and the royal family were notified before a public announcement was made by Kensington Palace on Twitter.
"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," Kensington Palace said in a statement.
In keeping with tradition, a statement was later posted on an easel in the forecourt of Buckingham Palace, just as it was after George and Charlotte's births.
Bells will toll, and there will be the traditional gun salute as the country celebrates the new heir.
The new baby's place in the royal family
History was made with the birth of William and Kate's third child as Charlotte became the first female to retain her claim to the throne, regardless of the baby’s gender.
The Succession to the Crown Act 2013, which was passed when Kate was pregnant with George, states that succession to the throne would be based wholly on birth order, not gender.
George is third in line to the throne and Charlotte is currently fourth in line to the throne.
William and Kate's third child is now fifth in line to the throne.
Prince Harry, 33, is now the sixth in line to the throne.
Like George and Charlotte, this child is designated as His Royal Highness and will have the title of Prince.
Delivery at the Lindo Wing
Kate had all the amenities of a five-star hotel inside the Lindo Wing, including freshly-prepared meals and afternoon tea service and champagne available for those who request it.
Birthing packages at the exclusive Lindo Wing start at 5,900 pounds, or around 8,300 U.S. dollars, for a one-night stay, with a standard room package. Deluxe packages at the hospital start at 6,275 pounds, or nearly 9,000 U.S. dollars.
The Lindo Wing is where the late Princess Diana also delivered both William and Harry.