The publication cites a rule that was established by King George V in 1917 that read: "…the grandchildren of the sons of any such sovereign in the direct male line (save only the eldest living son of the eldest son of the Prince of Wales) shall have and enjoy in all occasions the style and title enjoyed by the children of dukes of these our realms."
Under current guidelines, great-grandchildren of the monarch are not princes or princesses, except for children of the eldest son of the Prince of Wales.
This is why Prince William and Kate Middleton's children are Prince George, Princess Charlotte and Prince Louis.
Charles currently has five grandchildren in total, with Archie seventh in line to the throne, and Lili is eighth.
Meanwhile Prince George is third in line to the British throne, his sister Princess Charlotte ranks fourth, and his brother Prince Louis fifth in line.
William and Kate's children are currently the only great-grandchildren of the Queen's to carry the titles of 'prince' and 'princess', as well as the only grandchildren of Charles.
The conversion as to why Meghan and Harry's kids don't carry royal titles started during their tell-all interview with Oprah Winfrey back in March, where Meghan revealed there was a conversation about titles ahead of Archie's birth.
"They were saying they didn't want him to be a prince or princess, which would be different from protocol, and that he wasn't going to receive security," Meghan said.
While reflecting on the fact that baby Archie wasn't given a royal title, Meghan admitted there had also been talks about "how dark" his skin colour might be.
"In the months when I was pregnant, all around the same time, so we have in tandem the conversation of he won't be given security, he's not going to be given a title, and also concerns and conversations about how dark his skin might be when he's born," Meghan said.