Prince William's first name was chosen by his late mother, Princess Diana - but we would be calling him something else if his dad Charles got his way.
During an interview for Andrew Morton's book Diana: Her True Story, which was published in 1992, the late royal revealed she chosen both of her sons' first names.
That doesn't mean that Charles didn't have some ideas - but Diana simply wasn't keen on them.
Asked who picked the names, she said: "I did". She added: "I chose William and Harry but Charles did the rest. He wanted Albert and Arthur and I said no. Too old!"
Diana also picked Harry's name - but his legal name is actually Henry.
Harry was born on September 15, 1984, with his full name Prince Henry Charles Albert David. For official announcements, such as the engagement to Meghan Markle, he was always called Henry.
In 2022 the former royal joked about his real name in a chat with the winners of the WellChild Awards. "My name is Henry as well," he told a child called Henry. "But everyone calls me Harry. I have no idea why."
Harry is the diminutive form of Henry, a popular nickname that dates back to medieval England. Most monarchs given the name Henry in the past have been nicknamed Harry, including the infamous Henry VIII.
With Queen Elizabeth II and King Charles III keeping their first names when they ascended to the throne, William is widely expected to become King William V. But he will have the option to choose a 'regnal name', which doesn't have to be his first name but could be a middle name or another moniker.
Queen Victoria was the first to start this tradition - she was christened Alexandrina Victoria - but when she took the throne she chose to go by her middle name. Her son Prince Albert followed in her footsteps when he became King after her death in 1901, choosing to be King Edward II.
Queen Elizabeth II's father also made the swap when he became King, going from Albert - or Bertie as he was known to loved ones - to George VI. This might have been to honour his father, George V, who had been popular during his own reign, and create a sense of continuity after the shockwaves caused by the sudden abdication of Edward VIII, his elder brother.