VIDEO: William and Kate's Harry Potter Wand Duel!

WPA Pool

William and Kate truly let their hair down on a tour of the new Warner Bros studio in the UK today, taking part in a Harry Potter-style wand duel on a day of fun and games while experiencing the movie giant's new visitor tour.

The young royals - along with their brother Harry - were introduced to Harry Potter author JK Rowling and the couple were given a lesson in how to cast spells with wands - then duelled against each other.

William uttered the famous phrase "expelliarmus" to rob his his wife of magical power as nine children representing charities helped by the couple's foundation looked on.

William earlier joked about taking over the Batman role with Josh Berger, after having a go on the bat bike, president and managing director of Warner Brothers UK, Ireland and Spain, telling him: “Christian Bale’s getting old and tired ... I will stand in if I have to.”

The Duke, who is president of Bafta, said in a speech: “I’m over the moon just to have seen the real Batmobile and Batpod... you don’t do baby seats for those cars, do you, by any chance?

“On the other hand, Harry’s just excited to see a real-life talking owl in the Harry Potter studios. I haven’t told him yet that Harry Potter is fictional, so please keep the secret for a little longer.”