They started out as friends. Now, Life & Style has learned, Justin Theroux and Selena Gomez's relationship has taken an unexpected turn into something more serious.

"They've known each other for years through their manager," a source explains. "Initially, they leaned on each other for emotional support after going through messy breakups." Justin announced his split from wife Jennifer Aniston in February while Selena parted ways — again — with pop star Justin Bieber in March.

jennifer aniston and justin theroux getty images

In recent weeks, though, "they've become closer than ever," says the source. "It's turned into something more than friendship." Despite a 21-year age difference (he's 46, she's 25!), says an insider, "Selena and Justin are falling for each other." Friends think that’s a mistake — and warn that if Justin and Selena become a full-fledged couple, it will end badly.

Selena, Justin and Jen all share the same manager, Aleen Keshishian — and Jen, who views Selena as a friend is already aware that her ex and the pop star-actress have been hanging out. "Jen," the source adds, "is not happy about it." After all, Jen wasn't just a friend to Selena, "she was a mentor."