The "Sorry" singer celebrated restaurateur David Grutman's belated 36th birthday on Sunday evening, joining the club owner at his STORY nightclub in Miami, Florida.
Bieber hosted his Purpose World Tour after party at the club, and even sang a b-day song for Grutman, who shared his thanks (and a video of the performance) to Instagram.
The 22-year-old singer also shared a short clip of the celebration from inside the DJ's booth as he danced and sang along to Rihanna's "Work."
One of Bieber's former rumored romantic interests was also in attendance at the party: Kourtney Kardashian, who was joined by friends Larsa Pippen and Jonathan Cheban. According to an eyewitness, Kardashian and Bieber spent some time hanging out and chatting in the DJ Booth during the festivities
Earlier that day, Bieber hung out in Miami Beach, where the pop star partook in some wild wakeboarding.
Aside from his tighty-whities, the singer stayed (somewhat) safe in a neon-green life vest, and that's pretty much it. At least those Miami waters are warm this time of year.