It looks like Selena Gomez is back to keeping tabs on her ex Justin Bieber since her split up with Zedd!

The 22-year-old pop star threw some major shade at her ex-boyfriend after he shared a sexy photo of Ashley Moore via Instagram and hinted that he's thinking of hooking up with her.

Bieber, 21, posted a pic of the 21-year-old model, along with the caption: "Sometimes I wonder."