A hoard of photographers was already camped on the steps of the private King Edward VII hospital in central London where Kate was admitted yesterday.
Today one English daily newspaper dedicated 12 pages of articles to the announcement while others carried pages and pages of discussion about the history of royal births, who will be appointed nanny and where the child will go to school and what name it will be given.
The couple, both aged 30, were forced to make the announcement early because of Kate's medical difficulty, unleashing a media fever as a result.
They had not even told their own families, including Queen Elizabeth, and had to rush to do so before the hospital admission. Immediately they were congratulated by heads of state from across the world with President Obama one of the first to offer his good wishes.
The baby is already making history as the third in line to the throne, regardless of whether it is a boy or a girl, after the government decided to change the rules of royal succession last year.
The child will one day be head of state for 16 nations, head of the armed forces and Supreme Governor of the Church of England.
In the meantime, Kate is being cared for by Marcus Setchell, who was surgeon-gynaecologist to the queen until 2008 and delivered Sophie, Countess of Wessex's two children.
On a day of drama, Kate, who married William in April 2011, was rushed to the private hospital from her parents' home in Bucklebury, Berkshire, after suffering a bout of severe morning sickness.
William was by her side and travelled in a car with her to the hospital where she is expected to remain for several days after which she will rest at home until she recovers.
The couple had originally hoped to keep the announcement secret until just before Chirstmas as Kate is understood to be less than 12 weeks pregnant.
But they decided to inform their family and then the rest of the world amid fears that the visit to the hospital would soon leak out.
The queen and the rest of the royal family and the prime minister David Cameron were told just just before the press announcement at 4.01pm
The couple had declined the offer of an ambulance and used their own car to go to the hospital where Kate walked in and was said to be in good spirits.
The queen, Prince Philip and Prince Charles and members of both families are delighted with the news, said a spokesman.
St James's Palace would not say when the couple became aware of the pregnancy, only saying "recently".