Ubisoft have been known to use celebrities for their Just Dance series, with Just Dance 3 being featured in the music video for Katy Perry's Last Friday Night. Now it's time for Bieber to make his mark... by hiding behind a one way mirror and watching girls dance to his music.

Various groups of young girls were roped into a research focus group, happy to spend their day playing unreleased dancing games. Well, that's what they thought was the case anyway, instead what happened was half way through the song Bieber burst in for...well, we're not sure why. 

Needless to say, they were all pretty happy and enjoyed dancing with the man himself.

The face of true happiness, pictured left. 

Just Dance 4 is available now and is doing fairly well, managing to climb into the All-Format top 10 at #4, the Wii version accounting for 91% of the sales.