Kate Middleton is pregnant with her second child, Buckingham Palace said on Monday.
There was no information on when the next child of Britain's Prince William, grandson of Queen Elizabeth, and his wife is due.
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The couple's first child, Prince George, was born in July last year amid a huge international media frenzy. William is second in line to the British throne, with George third.
"The Queen and members of both families are delighted with the news that their royal highnesses are expecting their second child," Buckingham Palace said in a statement.
"Many congratulations to the Duke and Duchess of Cambridge. I'm delighted by the happy news that they're expecting another baby," British Prime Minister David Cameron said on his Twitter feed.
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