It’s the moment the nation has been waiting for: the Duchess of Cambridge has announced that she is pregnant.

The Queen, the Duke of Edinburgh and the rest of the Royal family are said to be ‘delighted’ with the news that the Duchess will be having a baby in May, June or July.

It's understood that the Duchess is not yet 12 weeks pregnant - the usual stage for announcing a pregnancy – and that she and Prince William had wanted to wait to reveal the news, but decided to release the news to avoid speculation about her condition when she was admitted to hospital today with an acute case of morning sickness.

Royal sources have so far not said how many weeks pregnant the Duchess is, but June or July next year seem the most likely time for the new arrival to appear.

She has been advised to take a lot of rest – something that she didn’t get much of last week due to a slew of public appearances.

On Friday she visited her former school St Andrew's in Berkshire, meeting current pupils and even playing a quick game of hockey in a tailored Alexander McQueen frock coat which, despite its nipped-in shape, did not reveal her pregnancy.

Earlier on last week, she wore a buttoned up Mulberry green silk dress to open the new Treasury Gallery of the Natural History Museum and a pale pink coat on an official visit to Cambridge, which were equally concealing.

The news comes after the Duke of Cambridge aroused suspicion after saying, ‘I’ll keep that!’ when presented with a babygro by a member of the public just last week.

In a change to Royal protocol, the baby will be the heir to the throne whether it is a boy or a girl. In previous generations boys were favoured even over older sisters. It will be the third in line to the throne.

See the Duchess of Cambridge's style file