Singer JUSTIN BIEBER had his 19th birthday celebrations ruined by an alleged night-club bust-up on Friday night (01Mar13).

The Canadian heartthrob, who is currently touring the U.K., held a circus-themed bash at London's Cirque du Soir to mark his big day, and invited his rumored new girlfriend, British singer Ella-Paige Roberts Clarke.

But just hours after excitedly tweeting about his "big night ahead", the Baby hitmaker took to his Twitter.com page and branded it his "worst birthday" ever.

Bieber did not expand on the dejected post but sources tell Eonline.com his evening took a turn for the worse after a confrontation between Bieber's entourage and club security, which resulted in the pop sensation and his entire party making an early exit after just a few minutes inside the venue.

Bieber and his pals, including Will Smith's son Jayden Smith, are said to have stopped off at a McDonald's before then returning to The Langham hotel.