British royals have many different names ranging from official titles, formal names, nicknames, and honorariums.
Even the names that you think of as official often are not.
Sometimes the reason is simple, such as with the Duchess of Cambridge and wife toPrince William.

Kate is a common nickname for Catherine, so this in itself isn’t unusual.
The same goes for His Royal HighnessPrince Harry.
Harry’s full name is actually Henry Charles Albert David.

Senior royals typically have lengthy first names which are “shortened” upon taking the throne.
Born Rachel Meghan Markle, she typically answers to her middle name.
The middle name use, once again, is not limited just to modern royals, however.
Queen Victoria also had a lengthy and lesser-known first name.
The famed queen of the United Kingdom, Queen Victoria’s full name was Alexandrina Victoria (viaBiography).
Why she chose her middle name upon coronation may be explained by a Newcastle scholar (viaQuora).
These royals don’t use their real first names but the reasons why vary.
For some, the answer seems simple, and for others, it may long remain a mystery.