'King James' breaks royal protocol with friendly photo of Kate and William

NBA star LeBron James didn't get the royal memo when he wrapped his arm around the Duchess of Cambridge as they posed for a photo after a game in New York.

The Cleveland Cavaliers player known as "King James" apparently broke royal protocol when he put his arm around Kate's shoulder in the post-match photo.

James gave the couple a Cavaliers shirt marked Cambridge and another for their one-year-old son Prince George.

"This very moment will be forever remembered and put up in my house. It's all good and all smiles on this side," James wrote on his Instagram page next to a photo with the royal couple.

Royal watchers were quick to remark that the friendly gesture breached an unwritten rule to not touch a royal during a meeting.

It's not the first time world leaders and celebrities have been criticised for their behaviour around the British royal family.

In 2011, US President Barack Obama was criticised for speaking during a rendition of the national anthem during a meeting with the Queen.

Former Australian Prime Minister Paul Keating earned the nickname “Lizard of Oz” after he put his arm around the Queen during her 1992 tour of Australia.

Additional reporting AFP