For the first time in history, a female royal’s spot in line to the throne won’t be bumped by the arrival of a younger brother. Thanks to the Succession to the Crown Act 2013, birth order determines who will become the next king or queen of the U.K., regardless of gender. Had it not been in place, Charlotte, who turns 3 on May 2, would have lost her spot if mom Kate Middleton had given birth to a boy.
The legislation was first passed while Princess Kate was pregnant with Charlotte’s brother Prince George, now 4. It affects all royals born after Oct. 28, 2011, and also removed the disqualification placed on those arising from marriage to a Roman Catholic.
Until 2013, older sisters would be moved down a spot in the order of succession if their parents had a younger son — like with Princess Anne after the birth of Prince Andrew and Prince Edward.
Currently, Prince Charles is the heir to the throne after his mother, Queen Elizabeth II. Prince William is second, with his kids Prince George and Prince Charlotte in the third and fourth positions, respectively. The new baby boy is fifth in line to the throne.
With his arrival, Prince Harry is now sixth in line, and Prince Andrew, Princess Beatrice and Princess Eugenie will all move down a place in the line of succession with the arrival of William and Kate’s younger son.
The royal couple announced they were expecting baby No. 3 in September 2017, and Princess Kate was admitted to the hospital on Monday, April 23, in the early stages of labor.
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Though she stepped out with William for Easter service, the 36-year-old mostly nested over the past few weeks in Apartment 1A of Kensington Palace and helped her children adjust to the idea of a baby brother or sister.
Both kids are “excited” for the impending addition, a friend told PEOPLE while noting, “Charlotte, as the youngest, may find it hard.”
Kate “feels it’s an incredible privilege to be a mum,” added Peter Fonagy, head of the Anna Freud National Centre for Children and Families.