The Duke and Duchess of Cambridge are expecting their child in April, they have revealed.
Kensington Palace said William and Kate were "delighted" to confirm the month their third child is due to be born.
The Duke and Duchess of Cambridge are delighted to confirm they are expecting a baby in April 2018. pic.twitter.com/jOzB1TJMof— Kensington Palace (@KensingtonRoyal) October 17, 2017
The new royal baby should arrive the month before the Cambridges' daughter Princess Charlotte turns three.
But Kate is believed to have gone beyond her due date with both Prince George and his sister.
The Duchess gave birth to George and Charlotte at the private Lindo Wing at St Mary's Hospital in Paddington, central London, and will be expected to do the same, unless she opts for a home birth.
The new baby will be born fifth in line to the throne, pushing uncle Prince Harry into sixth place. With the Duchess believed to be just over 12 weeks pregnant, it is likely the baby is due around the end of April.
The prince or princess could possibly arrive on William and Kate's seventh wedding anniversary on April 29 or close to Princess Charlotte's third birthday on May 2.
It is thought Charlotte's birth was overdue but if the Duke and Duchess' third child is born early it could coincide with the 92nd birthday of its great-grandmother the Queen on April 21.
Soon after the news of the pregnancy was revealed in September, William revealed there was "not much sleep" being had at the main family home of Kensington Palace as Kate fought her severe morning sickness.
"We need Catherine to get over this first bit and then we can start celebrating," he said at the time. "It's always a bit anxious to start with, but she's well."
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The couple are due to visit Norway and Sweden on an official visit early in 2018. The official trip was originally scheduled for next month, but has been delayed because of Kate's sickness.
William is going ahead with a solo trip to Finland in November, being committed to the schedule in order to mark the centenary of the country's independence in 2017.
Depending on the exact date of the joint tour, Kate could be heavily pregnant when she makes the trip with William to Norway and Sweden in the depths of the Scandinavian winter.
She made a surprise appearance at a royal engagement on Monday when Paddington Bear asked her for a dance - and she revealed she was fleet of foot.
Duchess of Cambridge dances with Paddington Bear
Kate and the famous children's character twirled and shimmied on platform one at London's Paddington station, where Michael Bond's creation was found.
The impromptu ballroom dancing-style exhibition happened as Kate, the Duke of Cambridge and Prince Harry waved off a group of children from the station, as they embarked on a day trip in a vintage carriages pulled by a steam locomotive.
Kate made a surprise appearance at the event, where the youngsters met some of the stars of the new Paddington II movie - including Hugh Bonneville.
The children taking part were selected by members of the royal trio's Charities Forum - with many going through difficult times in their lives.
William, Kate and Harry boarded the British Pullman to talk to the youngsters before the train took them on a journey through the English countryside.
Later, as they waited to wave them off, Paddington Bear, complete with his famous duffle coat and hat, began dancing in front of them to music from a calypso band and, when he offered his hand to Kate, she took it.
The Duchess may have towered above the famous bear but they moved in time together and Paddington even twirled Kate around as the dance ended.
Still in character, the actor inside the bear, who declined to give their name, said: "She's a right good mover, and I think she could win Strictly Come Dancing - if she was in it."