The Nickname Prince George And Princess Charlotte Call Prince Louis
Despite all the royal rules and the strict protocols, the royals have never shied away from giving each other nicknames, usually something funny or endearing. Recently, according to The Daily Mail, Prince George and Princess Charlotte have an adorable nickname they have to their younger sibling Prince Louis. “Lou Lou”-which they have apparently been using ever since he was a little baby.
But the other two have their own nicknames as well. Prince George is known as “PG” and “Tips” at school, a reference to the popular tea brand PGTips and Prince George’s initials.
“The name has been such a hit that William and Kate have both adopted the nickname for him at home, too.” -a source reports.

On the other hand, Princess Charlotte, who attends the same school as her brother George-Thomas’s Battersea in London-is usually called “Lottie” by her schoolmates, a name that her mother Kate Middleton also uses at home.
Kate is actually a nickname itself, with the Duchess of Cambridge’s full name being Catherine. Prince William also had his own nickname when he was a child, with his mother Princess Diana calling him “Wombat”.
“It began when I was two,” William said in a 2007 interview with NBC. “I’ve been rightfully told because I can’t remember back that far. But when we went to Australia with our parents, and the wombat, you know, that’s the local animal. So, I just basically got called that. Not because I look like a wombat—or maybe I do.”
Who knows what other nicknames the Cambridge children have for each other (probably some unflattering ones as well, as siblings go), but as time goes on they forget some and makeup others, which hopefully we will find out about in the future.