The Duchess of Cambridge, 31, was admitted into a London hospital early Monday in the early stages of labor, a palace official confirmed.
With her husband, Prince William, at her side, Duchess Kate was taken to a private wing of St. Mary's hospital, the same London facility where William and his brother, Prince Harry, were born.
"The duchess traveled by car from Kensington Palace to the Lindo Wing at St Mary's Hospital with the Duke of Cambridge," according to a statement released by royal officials.
The infant will be third in line to the British throne, after the child's father and grandfather, Prince Charles.
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Once the baby is born, the news will be shared with Queen Elizabeth, Prime Minister David Cameron, and the Middleton family before it becomes public.
A birth announcement written on official Buckingham Palace letterhead will then be driven to the palace, where it will be placed on the same easel used to announce Prince William's birth 31 years ago. In addition, the UK Ministry of Defence will mark the royal baby's birth with two gun salutes – a traditional sign of respect – at London's Green Park and on Tower Wharf at the Tower of London.
Neither the duke nor duchess claimed to have known the baby's gender before Kate went into labor, palace officials have said. Earlier this year, Queen Elizabeth took steps to update a century-old rule to make it easier to grant the child the title "princess" if she is a girl. Otherwise, a daughter would have only been allowed to receive the title, "lady."
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If the baby is a girl, she will become only the sixth woman to be crowned Queen in her own right in over 1500 years of the British monarchy.
In England, thousands of Britons placed wagers on any possible detail related to the baby in the past several weeks. Interest around the world also surged as Kate drew closer to her mid-July due date, with many countries making arrangements to publicly celebrate the baby's birth.
In addition to keeping the world anxiously awaiting, the royal baby watch also kept the monarchy restless.
"I hope it arrives soon because I'm going on holiday," Queen Elizabeth joked during a July 17 visit with schoolchildren.