Selena Gomez reportedly acts like ''a completely different person'' around Justin Bieber.

The 'Come & Get It' hitmaker, 21, reunited with her on-again, off-again boyfriend, 20, of more than three years last month, despite checking into a rehab facility in January in a bid to finally get over him, and her friends are allegedly worried by her behaviour.

A source told gossip website ''Selena is now acting a little brainwashed and not challenging a thing Justin says. There was a time not long ago where they were fighting and arguing about their relationship, but now she's like a robot and completely in his thrall.

''Whatever he did to keep her from moving on from the relationship worked a little bit too well, because it's like she's a completely different person.''

The couple were inseparable at the Coachella Valley Music and Arts Festival in Indio, California last weekend.

Meanwhile, sources close to the 'Heartbreaker' singer are glad he has reunited with the brunette beauty, who recently fired her parents as her managers, as she is helping him get his life back on track after a few difficult months.

An insider recently said that the Canadian star is ''ready to make some changes in his life'' ahead of his court appearance in Miami on May 6, where he will face charges for Driving Under the Influence (DUI), resisting arrest and possessing an invalid driver's licence in January.