The Baby hitmaker thrilled the crowd at L.A.'s Club Nokia venue by showing up unannounced to perform with the Australian teen sensation.
Bieber performed with Simpson on his track Pretty Brown Eyes, much to the delight of the crowd, and he subsequently boasted about the gig in a post on Twitter.com, writing, "Surprised the crowd at my bro (sic) Cody Simpson's show tonight. Proud of him. He killed it! Great job Cody."
Bieber has been in the headlines for all the wrong reasons recently following a dispute with his California neighbours who claimed the singer was racing around their gated community at high speeds in his Ferrari, prompting a police investigation.