Royal historian Kate Williams has said that being the 'spare heir' in the royal family can be a difficult position.
Dr Williams described Princess Margaret as: "the example of someone who didn't enjoy being number two."
David Beckham has given some friendly advice to the Duke and Duchess of Cambridge ahead of their new arrival - get some more sleep!
After it was announced the Duchess of Cambridge is pregnant with her second child we look back at her last pregnancy spent in the spotlight.
Kate and William's second child will join second-born Royal children as being known as the "spare to heir".