LONDON — It is a historic moment for the British monarchy — the couple's first child will become third in line for the British throne, after Prince Charles and William, and should eventually become king or queen.
William and Kate entered St. Mary's Hospital in central London through a side door early Monday morning, avoiding the world's media. Palace officials confirmed her arrival about 90 minutes later.
Royal officials said they traveled by car, without a police escort, just before 6 a.m. Kate — also known as the Duchess of Cambridge — is expected to give birth in the private Lindo Wing of the hospital, where Princess Diana also gave birth to William and his younger brother, Prince Harry.
"Things are progressing as normal," the couple's spokesman said.
She will be looked after by a top-notch medical team led by royal gynecologist Dr. Marcus Setchell. Palace officials are not expected to provide many details about how her labor is progressing.
The baby is in line to become Britain's monarch and be recognized as head of state in 15 other countries, including Canada and Australia, playing a leading role in charting the future of the Commonwealth.
But little else is known, including how the baby will arrive — it is not clear if Kate will have a natural birth or deliver by a planned cesarean section — its gender and its name.
In London, the royal birth is a tale of two cities — a moment of history unfolding amid the frenzy of daily urban life.
Now that Kate is in the hospital, what can royal baby watchers expect next? How do royal fans find out when the infant has arrived?
The short answer: Ignore all rumors on social media until there is an official announcement from Buckingham Palace. Unless you are Queen Elizabeth II or a senior member of the royal family, you will have to rely on a small piece of paper to get confirmed news that the baby is born.
Protocol requires that the queen be informed about the birth before the general public is told.
Following a time-honored royal tradition, the world will first read about the birth from a small bulletin posted in front of Buckingham Palace. It was the exact way officials announced the birth of Prince Charles in 1948 and Prince William in 1982, though this time around the monarchy has moved with the times and added social media as an easier way to reach more people.
The British react
Outside the hospital, Londoners slowed their daily rush on a scorching summer day to take a quick picture and wonder at the vast media throng, then moved on.
Two miles away at Buckingham Palace, the news seemed more momentous, an extra jolt of history to the royal pomp and pageantry that attracts tourists in their thousands each day. They may no longer wield political power, but Britain's royals are unsurpassed as celebrities and cultural icons.
"They're sort of the celebrities of the world," said Anne Frey, a beautician from Madison, Wisconsin, watching the daily Changing of the Guard ceremony with her husband.
Excitement for the imminent royal baby was strong among the crowds lining the black iron gates to watch soldiers in high bearskin hats, sweating stoically under their scarlet tunics, march behind a brass band into the palace grounds.
"We can tell our kids one day that we were here when it happened," said Jill Muencz, a tourist from Cleveland, Ohio.
"It's fantasy," she added. "We don't get to experience all that" as Americans.
The royal labor dominated British news bulletins Monday, as media from around the world provided nonstop comment, color and speculation from outside the private Lindo Wing of St. Mary's Hospital, around the corner from London's Paddington Station.
Prime Minister David Cameron said "the whole country is excited" — and while that may be politician's hyperbole, there was a sense that the birth of a future monarch was a feel-good event to add to a long spell of hot, sunny weather and British sports successes at Wimbledon, the Tour de France cycling race and in the Ashes cricket competition.
Few Britons were willing to go as far in their royalism as Terry Hutt, a 78-year-old carpenter from Cambridge in eastern England, who has camped outside the hospital for 12 days, sleeping outside the hospital on a bench covered with a Union Jack blanket.
Hutt, who is proud to have met every royal from the late Queen Mother on, said he was doing his bit for Britain by camping outside the hospital in his red, white and blue Union Jack suit, holding flags and congratulatory banners.
"To me, the royal family play a very, very important role," he said. "Visitors from all over the world haven't got a king and queen. It's a plus for us."
As London commuters rushed past the hospital to work, Pascal Faure, a maintenance contractor originally from South Africa, stopped to snap a picture on his phone for friends at home and in Australia.
"It's part of their heritage, I guess, their culture," said Faure, who claimed his own tenuous royal connection: "Apparently my third cousin once removed is Chelsy" Davy, Prince Harry's former girlfriend.
He also had more insight than most into the 5,000-pound ($8,000) -a-night private wing where the Duchess of Cambridge is giving birth. He fixed the air-conditioning there last week — a good thing, too, as Monday was scheduled to be the hottest day of the year in London.
"If the air-con stops working, I'll probably be the one to go in," he said.
The outpouring of affection for the royal infant is a sign of how thoroughly Britain's royal family has rebuilt its image in the eyes of its subjects since the low point that followed the death of Princess Diana in a car crash in 1997. Diana had been popular, glamorous and — in the eyes of many — badly treated by the royal "Firm."
Sixteen years on, support for the monarchy is riding high after William and Kate's 2011 wedding and last year's Diamond Jubilee celebrations for Queen Elizabeth II's 60 years on the throne.
For non-Britons, the emergence of an attractive young generation that includes William, Kate and soldier-socialite Prince Harry has given the clan a mix of glamour and celebrity that is hard to resist.
"We like to pretend we have a king and queen," said 17-year-old Maddie Cruse, from Helena, Montana, as she stood outside Buckingham Palace. "Since we don't have a king and queen, we borrow yours."
Like many visitors, Cruse was well versed about recent changes to royal rules that mean a daughter will not lose her place in the royal succession if William and Kate later have a son. Boy or girl, the baby will be third in line to the throne behind Prince Charles and Prince William and is likely to be monarch one day — a fact that is lending an extra sense of history to the birth.
"I hope it's a girl, because it's the first royal that could assume the throne as a girl," Cruse said. "And she'll be a princess, and we'll get to see all the cute little clothes."