The one royal rule Kate and Will had to follow after welcoming Prince Louis this week

There's a lot to be considered when a new royal baby comes into the world.

For Kate and William, their main concern on Monday when Kate went into labour might have been the safe delivery of the baby but for the royal family as a whole, there's lots of official protocol in place that has to be followed. The number one rule for new arrivals is that the Queen, as head of the family, must be first to know when the baby is born. Most couples probably ring their own parents first but Will has to bypass his father Prince Charles and call his grandmother, Queen Elizabeth, first with the news before he can tell anyone else. The Sun reports that the prince rang her on an encrypted phone when Prince George was born. It's one of the only traditions surrounding a royal birth that's lasted up to the modern day. For example, royal babies were always traditionally born at home before Princess Diana came along. The Queen gave birth to her four children in Buckingham Palace but Diana broke the mould by choosing to have William and Harry and the Lindo Wing in St Mary's Hospital in Paddington, the same place Kate gave birth to all of hers. William and Kate have also made a big change to how royal births are announced. The news always came first on an easel outside Buckingham Palace but Prince George's birth was revealed on Twitter before anywhere else.