This is why Prince William and Kate's third child will make history if it's a boy

It was announced this week that Kate, the Duchess of Cambridge is expecting her third child with husband Prince William.

And while Kate's pregnancy itself will be the main focus for a good few months, the end result could also have a significant impact on the British chain of royal succession.

Already parents to four year old Prince George and two year old Princess Charlotte, if Kate and Will's third child is a boy, history will be made thanks to a law put in place in 2015.

Before this date, the baby's gender would have taken precedence over age when it came to their place in line to the throne, as has always been custom previously, but now for the first time, if the couple welcome a son, older sister Charlotte will still remain ahead of him in the line of succession.

So the order, as it stands after the new child's birth, will be Prince George, Princess Charlotte and the new sibling, behind their grandfather Prince Charles, who is first, and father Prince William, who is second.

The law enforcing the new gender equality rule was first passed in Britain in 2013, and read: 'In determining the succession to the Crown, the gender of a person born after 28 October 2011 does not give that person, or that person's descendants, precedence over any other person (whenever born).'

However, it had to be approved in every country where the British Monarch is a recognised as head of state, as reported by the BBC. This process took until 2015, when the rule finally came into force.

The news that Kate and William were expecting again also meant that Prince Harry will be bumped down another rung to sixth in line to the throne.

Shortly after the couple's baby joy was confirmed in a statement from Kensington Palace, Harry, 32, told reporters that he was 'very, very' happy for his brother and sister-in-law.