New royal baby would be fifth in line to throne, but unlikely to be crowned
The third child of royal couple Prince William and Kate Middleton is fifth in line to the throne and unlikely to ever succeed to be crowned sovereign, according to experts.
The new prince or princess was announced yesterday by the couple after the duchess was forced to pull out of a public engagement with severe morning sickness.
She is less than 12 weeks' pregnant, according to Kensington Palace.
The duchess, who is being cared for at the palace, is suffering from hyperemesis gravidarum, as she did in her previous pregnancies.
Just weeks ago, she joked about having a third child while on a tour of Poland and Germany with the prince and their first two children, George and Charlotte.
After being given a present designed for newborns while in Warsaw, she laughed and turned to her husband, saying: "We will just have to have more babies."
Kensington Palace said in a statement: "Their Royal Highnesses the Duke and Duchess of Cambridge are very pleased to announce that the Duchess of Cambridge is expecting their third child.
"The Queen and members of both families are delighted with the news."
The duchess had been due to visit the Hornsey Road Children's Centre in London to hear about the mental health impact of becoming a mother.
Clarence House said of heir to the throne Prince Charles and the Duchess of Cornwall: "They are delighted at the news."
The announcement comes as they are preparing to send their eldest child off to school for the first time. Four-year-old future king George starts at fee-paying independent school Thomas's Battersea in south London on Thursday.
As a sibling to both future king Prince George and "spare to the heir" Princess Charlotte, the Duke and Duchess of Cambridge's third child is unlikely ever to be crowned sovereign.
If the Cambridges' third child is a boy, he will no longer be allowed to jump ahead of older sister Charlotte in the line of succession due to changes in royal inheritance laws.
The royal couple are expected to keep it classic when choosing a name for their new child - just like they did for Prince George and Princess Charlotte.
If the baby is a girl, they are likely to pick a name such as Alice - which was the name of one of Queen Victoria's daughters - or Victoria after the baby's long-reigning ancestor.
Other suggestions include Alexandra or Mary, Queen Elizabeth's two middle names.
The name has been the most popular girls' name in England and Wales since 2011.
Elizabeth - after the baby's great-grandmother the queen - has already been used as one of Charlotte's middle names, as has Diana in remembrance of the prince's late mother. Dorothy might be selected as a middle name in tribute to the duchess's maternal grandmother.
James is among the favourite predictions for a boy, along with Philip, which might be chosen out of respect for the prince's grandfather, the Duke of Edinburgh.