It wasn't such a happy birthday for Justin Bieber after all.

The pop star, who celebrated his 19th birthday on Friday, took to Twitter to lament to his more than 35 million followers that it had been his "worst birthday" ever.

Bieber had intended to throw a big bash at London's Cirque Du Soir nightclub, but things went south after an alleged confrontation between his entourage and club security.

Bieber and his friends left shortly after arriving, with conflicting reports about why the scuffle occurred -- including that Bieber was kicked out for bringing Will Smith's son Jaden, who at 14, is underage.

The star slammed those reports on Instagram, however. After posting a blank, black photo, he wrote, "The funny moment when people believe I brought underage people to a club.. U think Will is letting his 14 year old in a club, I don't think so."

Bieber went on to claim the real reason why he left the club was because of the club security's rough handling of his fans. "I love how the club wanted to give the press another reason to why we didn't stay at their weak a** club so they wouldn't look bad for me walking in and right back out..i said m[y] 'worst bday' but that was due to dummies pushing over my fans and being overly aggressive."

All was not lost for Bieber, however. In the same Instagram post he went on to write, "it wasn't the worst bday cuz all my friends from back home flew in I was just mad in the moment."