Canadian sensation Justin Bieber has a reputation for bringing surprise guests onto his stage, but during his show in Sydney today (April 28) he shocked the audience as Chris Brown walked out. 

The 17-year-old 'Baby' hitmaker was finishing off an acoustic performance of Brown's 'With You' when he turned around and introduced the star to the screaming crowd. The pair then gave a rendition of Brown's 'Look At Me Now', during which Bieber exercised his rapping skills. 

After the show, Brown tweeted:

"the show tonight was craaaaaazzzzzzyyyyyy!!!! @justinbieberLEGGGOO! shut it down"

Watch the exciting moment here: