Do you know about the ancient Royal tradition / Rule of, younger male siblings getting an automatic right to the throne over his older female siblings?

Until this was changed by the Parliament in 2011 during the Government of David Cameron, this was a long practice.

QE I

This was how the third child of Henry VIII, Prince Edward, became the King, and only after his death did his sisters Mary and Elizebeth come to the throne. Henry VIII famously married six times in search of a son to be his heir.

Edward VI became King, despite having two older sisters.

There were other examples in history too.

The incumbent monarch, Queen Elizebeth II was the first child and the oldest of the two daughters of King George VI. Her father ascended to the throne on the abdication of his older brother King Edward VIII.

Before QE II, the female monarch was Queen Victoria. She too was the only daughter of the fourth son (Prince Edward) of King George III. Prince Edward’s predeceased his father and other older brothers (including King William IV) who all died without lawful heirs and so Victoria became the Queen on the death of his uncle King William IV.

The new law altered the law of succession to the British throne came into force on 26 March 2015, approved not only by the UK parliament but also by the Commonwealth countries. The new law means Princess Charlette (daughter of Prince William) becomes 4th in line to the throne instead of 5th after her younger brother Prince Louis.

The next female monarch may not be in our lifetime as the next three heirs to the throne are males.

QE II with the next three heirs to the throne

Read this: https://thegreatbritishlife.com/mary-tudor/