Justin Bieber surprised his fans yesterday (June 27) by performing an acoustic rendition of his hit 'Boyfriend' outside a TV studio.

The Canadian singer had been filming for Jay Leno's talk show in California when a sizeable crowd of Bieber fans amassed outside the gates.

The teen star however rolled up in van and stood in its doorway alongside guitarist Dan Kanter, who then launched into an acoustic version of 'Boyfriend'.

Although Bieber was largely drowned out by the gaggle of girls watching on, the surprise set went down a treat.

Kanter tweeted about the performance:

"We played acoustic for all the fans waiting outside the NBC gates. Great to see how much JB appreciates his fans."

Watch Justin Bieber surprise his fans below: