The Succession to the Crown Act came into force on Thursday 26 March, marking the end of male primogeniture across the Commonwealth of Nations. The new legislation means that if the Duchess of Cambridge's second royal baby is a girl, she will not be overtaken in the line of succession by any younger brothers.
The three main changes under the law are that the order of succession will no longer be based on gender, a person married to a Roman Catholic can accede to the throne and that only the first six in line to the throne must seek the Sovereign's permission to marry. Previously all members of the royal family were required ask permission before marrying.
Changes to the Succession to the Crown Act have come into force across the 16 Commonwealth countries
Changes to the law were agreed in 2011 and passed in the UK in 2013. It was intended for the act to come into effect in all 16 of the Commonwealth realms at the same time, however, it has taken until now to become universally enforced.
The law acknowledges the date when the original changes were agreed and now states: "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)."
Two years ago, as royal watchers eagerly anticipated the birth of Prince William and Duchess Kate's first child, news surfaced that the succession law was about to change after 300 years.
If Prince George has a younger sister, she will not be overtaken by future younger brothers
In April 2013, the Succession to the Crown Bill was steered through the House of Lords and given to the Queen for final approval.
Deputy Prime Minister Nick Clegg, who was a vocal supporter of the bill since it was introduced at the Commonwealth Heads of Government meeting in Perth, Australia, described the change as a "historic moment".
"I am proud the British Parliament has taken this step to end centuries of religious and gender discrimination," he said. "The government will soon introduce the Succession to the Crown Bill, which will make our old-fashioned rules fit for the 21st century."