Update 3:35 p.m. EST: Kensington Palace says that the Duchess of Cambridge has given birth to a baby boy. The baby weighs 8lbs 6oz and was born at 4:24 p.m. Here's the full statement:

Her Royal Highness The Duchess of Cambridge was safely delivered of a son at 4.24pm.

The baby weighs 8lbs 6oz.

The Duke of Cambridge was present for the birth.

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.

Her Royal Highness and her child are both doing well and will remain in hospital overnight.

Earlier: Royalists and Anglophiles: The Duchess of Cambridge, the well-married commoner better known as Kate Middleton, is getting ready to have her and Prince William's baby, who will become third in line for the British throne. Clarence House, part of St. James Palace, Tweeted, "Her Royal Highness The Duchess of Cambridge has been admitted to St. Mary’s Hospital, Paddington, London in the early stages of labour."

Clarence House added, "The Duchess travelled by car from Kensington Palace to the Lindo Wing at St. Mary’s Hospital with The Duke of Cambridge." The Duchess was admitted around 6 a.m. and the couple's spokesman said, "Things are progressing as normal." FYI, labor can take hours or days!

Last December, the pregnancy was announced while also explaining that the duchess was in the hospital being treated for "Hyperemesis Gravidarum"—aka acute morning sickness. The excitement around a royal baby has prompted a tragic radio DJ prank, an insane media frenzy and impatient requests from the Queen for the tot to arrive before her holiday.

Once the baby is actually born, there's protocol. From The Daily Beast:

If the palace is able to control the news the way it is seeking to, then the first indication that the Duchess has given birth will come when an aide leaves the hospital carrying a sheet of paper detailing the baby’s sex, weight and time of birth. This will be handed to a driver and taken to Buckingham Palace.

The public will find out the details of the future heir to the throne when the notice is placed on an easel in the forecourt of the Palace. The same easel was used to display the notice of Prince William's birth.

The news will not be relayed by the palace's twitter feed for approximately half an hour, sources say.

The baby will be known as the prince or princess of Cambridge and will be, according to the AP, "recognized as head of state in 15 other countries, including Canada and Australia, playing a leading role in charting the future of the Commonwealth."

For some reason, many Americans are highly interested in royals (even making a royal baby in cake form), even the whole point of America was to get away from all that. A writer at the Guardian was amused about the fascination here: "The normally-sober National Public Radio has presented in depth explications of the kid's potential surnames (Cambridge? Mountbatten-Windsor? Saxe-Coburg-Gotha?), the 62-gun salute from the Tower, and an interview with Mail columnist Robert Hardman on the 2013 Succession to the Crown Act... The Washington Post, winner of 47 Pulitzer Prizes, broke the shocking inside story of human birth, quoting Janet Fyle, a 'professional policy adviser' at the Royal College of Midwives: 'The baby will come when he or she is ready.'" And NBC News has a Door Cam, so you can see when someone emerges from the door.

The AP also spoke to two teachers from New York, Maddalena Buffalino, 29, and Michael Savino, 32, who were in London and spotted "quizzing a pair of passing police officers about where the easel would be placed." Buffalino said she followed the royal baby news avidly, "Just being here is very cool. It's the history. We don't have it."

Brits are excited too: Douglas Johnston, an engineer from Glasgow, told the NY Times, "It is a glorious day and it is fantastic to be part of it... I am 30 so in my adult lifetime this is unprecedented and I may not get the chance to see this again."
Prince William and the Duchess of Cambridge were married in April 2011.