Kate banned from doing this when she greets the public

She may be on the most famous women on earth, but there’s one thing Kate Middleton can’t do that sets her aside from other celebrities.

The 35-year-old mother-of-two and her famous family are actually banned from singing autographs when they meet the public.

RELATED: Camilla and Kate clash over who will be the next King
RELATED: Inside Prince Harry's 'magical' proposal to Meghan Markle

Not only are they forbidden from scribbling their names on pieces of paper, but some of the family royal members also shun selfies.

According to royal insiders, the bizarre rule protects Kate Middleton and her crew from people forging their signatures.

Back in 2010, Prince Charles was famously asked by a father if the future King would sign a piece of paper for his young son.

“Sorry, they don’t allow me to do that,” he replied, before scrawling “Charles 2010,” on the paper.

Speaking to the Daily Mail at the time, Photographer Paul Williams said he often sees the royal politely decline signature requests.

“The long-standing rule remains in place for all royals because of the risk of the signature being forged,” he said.

Charles also apologized for his “shaky writing”, claiming he never writes standing up.

Likewise, Prince Harry is clear about what he will and won’t do for his fans.

Back in 2015 while visiting a war memorial in Australia, he told a fan he “hates selfies” and asked him to just take a normal photo of him.

“Seriously, you need to get out of it. I know you're young, but selfies are bad,” he said at the time.

There’s a long list of royal protocols which the family must follow, including no shellfish and no eating after the Queen has finished.

Want more celebrity, entertainment and lifestyle news? Follow Be on Facebook, Twitter, Pinterest, Tumblr and Instagram