When is Kate Middleton's due date? The Duchess of Cambridge is expecting her third child with Prince William. And the little boy or girl should arrive sometime in the spring. He or she will join 4-year-old Prince George and 2-year-old Princess Charlotte.

"Their Royal Highnesses The Duke and Duchess of Cambridge are very pleased to announce that The Duchess of Cambridge is expecting their third child," Kensington Palace said in a statement. "The Queen and members of both families are delighted with the news."

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Kensington Palace did not confirm Middleton's exact due date. Normally, pregnancy announcements occur at around the 12-week mark.

William Kate And The Kids Prince William and Kate Middleton's family is expanding once again (Photo: Retropix / Splash News).

However, sources say Middleton is still in the first trimester of her pregnancy. The news was announced earlier than usual because she had to cancel a planned appearance due to hyperemesis gravidarum. Middleton suffered from this acute morning sickness during her first two pregnancies, as well.

Since Middleton is still in her first trimester, the baby boy or girl is due between March and June of next year. In fact, there is speculation that the child was conceived during the Wimbledon tennis tournament in July. That would make her due date sometime in April or May.

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The Palace also hasn't revealed the sex of Middleton's third child. But fans making bets on the royal baby's name seem to think it's more likely she will have another girl. Bookmakers William Hill and Ladbrokes each say that the royal baby name most popular with bettors is Alice. The next most popular names on William Hill are Elizabeth and James, while Ladbrokes bettors favor Arthur and Victoria.

William And Kate Prince William and Kate Middleton have not revealed if they are having a boy or a girl (Photo: Retropix / Splash News).

"The early money suggests punters would love to see Kate and Wills welcome another little girl into their family, who is called Alice," Ladbrokes spokeswoman Jessica Bridge said in a statement. "It should come as no surprise to see fairly normal yet regal names top the betting."

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In the meantime, the Royal Family is excited about its new addition. William's brother, Prince Harry, told reporters on Monday that the pregnancy news is "fantastic, great. Very, very happy for them." He also said of his sister-in-law's illness, "I haven't seen her for a while but I think she's OK."

Do you think Kate Middleton is having a boy or a girl? Let us know your take in the comments section below!