Kate Middleton is unable to use this naughty nickname for Prince William in public

The Prince and Princess of Wales get the world talking on the regular, with the internet fascinated by their sweet relationship. And while the couple strive to stay professional in public and keep their intimate moments behind closed doors, they have been known to let it slip on occasion. 

This is particularly true when it comes to their pet names for each other.

Prince William is known to call Kate "darling", and his wife has been heard on several occasions calling him "babe" in public. But it was a naughtier nickname between the Prince and Princess that made headlines recently.

According to The Sun, Kate Middleton has a particularly hilarious nickname for her hubby, "Big Willy".

Yes, really.

The publication reported that she also used to call him "Baldy", and that Prince William had some sweet nicknames of his own for his wife, "Babykins" and "DoD" [Duchess of Dolittle].

While we certainly didn't expect this news, Prince William is no stranger to nicknames.

He is famously known as "Wombat" within the royal family - a nickname that was given to him by Princess Diana.

"I can’t get rid of it now," he has said of the sweet nickname. "It began when I was two. 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."

And to university friends, he is known as "Steve", going by the moniker at St Andrew's in order to stay under the radar.

This reportedly allowed Kate to talk to her friends on campus about her relationship with "Steve" and for their mutual friends to refer to "Steve and Kate's relationship" without arousing any suspicion - keep their business out of the royal rumour mill.

How many names can one man have?