Congratulations to Their Royal Highnesses Duke and Duchess of Cambridge, who have announced they are expecting their first child.

When the baby is born it will mean that Prince Harry is moved from third in-line to the British throne to fourth in-line.

If we follow the precedent of other recent Royal babies, such as Viscount Severn and Lady Louise (the Prince & Countess of Wessex's two children), William and Catherine's child will be given a title a day or so after the birth. Buckingham Palace will now be thinking of options for the child, but it will remain a secret until after the birth.

No details have been announced of where this birth will take place (a bit premature!) but it will be interesting to see whether the quasi-tradition of having the birth at St Mary's, Paddington occurs. Both Princes William and Harry were born here.

The current Royal Gynecologist (yes, that is a post) is Dr. Alan Farthing and it is expected (but not confirmed) that he will oversee the Duchess of Cambridge's pregnancy and the birth.

However, there is a break in precedent. If the baby had been born two years ago and it had been a girl then any brother that came along later would usurp its elder sister and have precedence in the line of succession. But due to a new agreement made last year at the Commonwealth meeting in Australia, this will no longer be the case.

This makes 2013's Royal baby a thoroughly modern heir!

Follow William Hanson on Twitter: www.twitter.com/williamhanson