Justin Bieber has slammed his 19th birthday celebrations as being the "worst birthday."The 'Beauty And A Beat' singer - who turned 19 yesterday(01.03.13) - had reportedly forked out £10,000 for a circus themed bash in London and invited 20 friends to join him in the capital but the party had to be cut short after the star's entourage clashed with security staff at the Cirque du Soir club, according to E!News.Jaden Smith, the 14-year-old actor who is the son of Hollywood power couple Will Smith and Jada Pinkett-Smith - was blamed for ruining Bieber's party.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."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.The singer's birthday was further ruined after he discovered his friend Lil Twist was pulled over by police while being behind the wheel of his Fisker Karma.TMZ reported the rapper had been stopped after making an unsafe lane change in the expensive sports car which costs over £100,000.View the gallery for photos of Justin Bieber's new love interest, as well as other related photos.