Demi Lovato pranked by comedian during royal meeting

Pop star Demi Lovato came close to breaking protocol during a meeting with Catherine, Duchess Of Cambridge after a British comedian urged her to grab the pregnant royal's baby bump.

The Skyscraper hitmaker was among the artists who took to the stage at the Royal Variety Performance in London earlier this month (Nov14) and she joined the line of performers to greet Prince William and his wife after the show.

Lovato was stood next to British funnyman Jack Whitehall as she waited to be introduced to the royal couple, and the comedian took advantage of the American's naivety by playing a naughty prank on her.

Whitehall explains to talk show host Jonathan Ross, "She (Lovato) was very nice, very sweet but American and didn't necessarily buy into my sense of humor and everyone is very nervous when the royal family are coming around and she asked me what the protocol was with the royal bump, 'Can we talk about the baby and stuff?', and as a joke I said 'The Duchess of Cambridge I think would be offended if you didn't have a little feel' as a joke."

However, Whitehall decided to step in and stop the prank when he realized the situation could turn serious.

He adds, "She takes it completely at face value and as Kate Middleton is coming along the line, I suddenly realize that we've got a situation here where either I need to step in and tell her that it was a joke and look like an idiot or potentially Demi Lovato from Frozen is about to get taken out by a police marksman, so I told her."

The interview on The Jonathan Ross Show airs in the U.K. on Saturday (22Nov14).