As the fourth in line to the throne, William and Kate's new baby will not be expected to be crowned sovereign.
He or she will join second-born Royal children as being known as the "spare to heir".
Their second-born will be a great-grandchild to the Queen
It will be a great-great-great-great-great-grandchild of Queen Victoria
Its birth will push Prince Harry down to fifth in line for the throne
The Duke of York will move to sixth place and princesses Beatrice and Eugenie to seventh and eighth
If the baby is a girl, it will be the first time a great granddaughter of a still-serving Monarch has been born in direct succession on the male line since 1897