Justin had the worst birthday after getting barred from Cirque Du Soir in London on March 1…

Now, a club spokesman reveals the real reason why Justin and his friends were asked to leave the venue.

Unfortunately Justin, 19, his friends, Jaden Smith, 14, and Ellapaige Roberts-Clarke, 17, were refused by Cirque Du Soir because they’re underage.

Justin allegedly left the venue after five minutes because he didn’t want to party without his friends.

“We, like all clubs in London, operate a strict age policy,” a club spokesman tells E! News.“As a few of the members of the party were under the suitable age of 18, the security team at Cirque Du Soir, London, clearly explained this rule and refused entry to the club for anyone who could not provide us with adequate proof of age. Justin Bieber visits Cirque Du Soir regularly, and he and his friends are always welcome, as long the members of the group are legally old enough to enter the club. This was simply a matter of regulation that we must adhere to.”

The club spokesman added, “We are very sorry, and understand it’s his birthday, but our hands are tied with local authorities and rules we need to follow as club to keep our license. We clearly didn’t want to give him the ‘worst birthday.’  He is a friend and previously was always welcomed with open arms.”