Clarence House Tweeted that the couple were “very pleased to announce” the duchess was pregnant again.

Kate, who is thought to be eight weeks pregnant, is suffering from acute morning sickness – and the news has been announced early because she was forced to pull out of an event at Oxford University today.

The Queen and members of both families were “delighted with the news” and Prime Minister David Cameron, Labour leader Ed Miliband and the Archbishop of Canterbury are among those offering their congratulations to the couple.

Kate suffers from hyperemesis gravidarum, which affects 3.5 per 1,000 pregnancies, and causes severe vomiting. It can lead to dehydration, weight loss and a build-up of toxins in the blood or urine, called ketosis.

The couple’s first baby, Prince George, turned one in July.

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