The 'Boyfriend' hitmaker was working on new material with his protégé Madison Beer at Miami's Hit Factory recording studio when his on-again-off-again girlfriend decided to stop by.
Justin had taken to Twitter earlier in the day to ask Madison if she was ready for her studio session.
He wrote: "Studio today. @MadisonElleBeer u ready? :) (sic)"
The 20-year-old star then followed up his message with some words of wisdom for his fans as he simply wrote: "Work hard everyday."
The threesome appeared to be getting on well as they all posed for a number of photographs which have been posted to an Instagram account which appears to belong to Madison's mother Tracie.
In one image Selena, 21, is seen with her arms around the 15-year-old star's waist while she pouts for the camera, and although Justin also posed with his young colleague, he and Selena do not appear to have taken any snaps together.
The pair - who are said to have split earlier this year after briefly rekindling their romance - have been keeping their fans guessing as to whether or not they are back together but as Justin is said to have gifted Selena with a ring last month it's been reported that they are definitely back on.