Will and Kate waited until their Diamond Jubilee tour was over before trying for a baby.
The royal couple - who, on Monday (03.12.12), announced they were expecting their first child together - decided to put their baby plans on hold until after Prince William's grandmother, the Queen, had celebrated her 60 years on the throne and they had been on a tour of the Far East as part of their Jubilee commitments.
Duchess Kate - who is also known as her maiden name of Kate Middleton - is currently in hospital suffering from acute morning sickness but the couple are thrilled with the news and think it's perfect timing.
A source told the Daily Mirror: "As far as everyone in the household is concerned this is wonderful news.
"Of course there is concern, and the announcement has come earlier than would otherwise have been the case, however next summer really couldn't be better timing for a baby.
"It was very sensible of them to wait until the Jubilee was over and it made sense for Kate not to be pregnant during the royal tour when she was taking malaria tablets."
Whether the baby is a boy or a girl, it will one day become monarch following a shake up of the royal succession law which previously meant a male would be able to leap-frog their older sisters to become the king of Britain and the Commonwealth.
British Deputy Prime Minister Nick Clegg said: "This is a very exciting day and brilliant news.
"And by happy coincidence we are working right now to put the finishing touches to laws that will update the very old-fashioned rules of succession and mean if they have a baby girl, she will succeed to the throne."