What Is A Regnal Name And Why Do Monarchs Use Them?
Throughout history, royals have been known to rule using their regnal name. It's the name that they use during their reign, and they are free to choose one when they accede to the throne. Significantly, it does not have to have any relation to their given name. However, regnal names are not solely for monarchs; popes use them too. For instance, Jorge Mario Bergoglio's regnal name is Pope Francis. Regnal names may come with a Roman numeral in instances when they have been used by prior reigning monarchs (via Royal Central).
Queen Elizabeth II chose to keep her given name when she became queen in 1952. According to Hello Magazine, when she was asked what she wished her regnal name to be, she simply answered, "My own, of course." Although monarchs are given the choice to keep their name or use a regnal name, there have only been a handful of instances in history when a name change occurred.
Regnal names in history
A monarch choosing a regnal name is quite rare. It's so uncommon, in fact, that in more than 200 years of British history, there have only been three royals who chose a different regnal name instead of their birth name during their reign (via Yahoo News). In 1837, at the age of 18 years old, Alexandrina Victoria became the queen of England. She chose her second name as her regnal name, and she is known as Queen Victoria in historical references. According to Town and Country Magazine, she always preferred being called by her second name or the nickname 'Drina.
Likewise, Queen Victoria's son, Albert Edward, changed his name when he acceded to the throne. However, the reasoning behind it had something to do with his mother. Albert Edward was named after his father, Prince Albert, who died in 1861. Queen Victoria somewhat blamed Albert Edward for her husband's death, as her son had a reputation for being a ladies' man and was reprimanded by his father two weeks before his death. For that reason, Queen Victoria didn't want her son to carry her late husband's name, and she unofficially banned any future king from using the name Albert, per Express. Albert Edward then chose his second name as his regnal name and became Edward VII.
Lastly, the third monarch who changed his name was Albert Frederick Arthur George Windsor, who chose the regnal name George VI as a tribute to his father (via Biography).