Los Angeles: Justin Bieber and Selena Gomez were at it again, and this time there were unintended beneficiaries ... some random people at a hotel bar who got to hear Justin serenade Selena for free.

The Biebs plopped his butt on a piano stool at the Montage hotel bar in Bev Hills Friday night and sang "My Girl" to his on-again-off-again-on-again-off-again-on-again-off-again GF.

After the mini-concert, they strolled through the empty streets of Beverly Hills.

It's the first time they've been seen together in more than a year.

Courtesy TMZ