Jaden Smith has been blamed for ruining Justin Bieber's birthday party.

The 14-year-old actor - who is the son of Hollywood power couple Will Smith and Jada Pinkett-Smith - was allegedly responsible for the Canadian popstar and his entourage's confrontation with security that led to them having to leave a London nightclub on Friday night (01.03.13) after just 15 minutes because they refused to let Jaden, who starred in 'The Karate Kid' remake, into the event because he is underage.

A source told USMagazine.com: ''There was never any mention of Jaden being there, so when he showed up, it caused problems. They could have stayed if Jaden left, but Justin wanted to be loyal to his good friend.''

The 'Beauty And A Beat' singer - who turned 19 yesterday - deemed it his ''worst birthday'' ever after he forked out £10,000 for a circus themed bash at Cirque du Soir nightclub.

Earlier in the evening he had been looking forward to a night out with Jaden and model Ella-Paige Roberts Clarke - who is rumoured to be his new girlfriend, and he shared his excitement on Twitter, writing: ''Gonna be fun tonight. Thanks to everyone for all the birthday wishes. 19!''

However he later posted: ''Worst birthday.''

The group went to McDonald's after leaving the nightclub before returning to posh hotel, The Langham, where he is staying during his time in the UK.