Royal protocol states that the Queen should always be greeted as Your Majesty or Ma'am, but the monarch's grandchildren have their own affectionate names to use in private.
According to Business Insider, Princes William and Harry use the informal term 'Granny' behind closed doors, and it's not the only nickname they have given their grandmother over the years.
In an article written for the Daily Mail, columnist Richard Kay looked back on William's younger years when he was growing up at Kensington Palace. "At two, William was boisterous and full of beans," Kay said, before he described one memorable occasion.
After a fall at, the Prince cried out for "Gary, Gary," Kay wrote. When a guest asked who Gary was, the Queen stepped in and explained: "I'm Gary. He hasn't learned to say Granny yet." While it's hard to imagine the Queen as a 'Gary,' it's definitely a lot easier for a toddler to say than the more formal alternative, Queen Elizabeth Alexandra Mary.