AceShowbiz - Following his split from ex-wife Jennifer Aniston, Justin Theroux has been hit with several dating rumors. Most recently, "The Leftovers" alum is allegedly romancing Selena Gomez as their friendship has taken an unexpected turn into a romantic relationship.

"They've known each other for years through their manager," a source explains to Life & Style. "Initially, they leaned on each other for emotional support after going through messy breakups." The actor announced his shocking split from Jennifer back in February, while Selena broke up with her on-and-off boyfriend Justin Bieber the following month.

According to the source, the 46-year-old actor and the 25-year-old former Disney darling have "become closer than ever" in recent weeks. "It's turned into something more than friendship." Despite a 21-year age difference, "Selena and Justin are falling for each other."

While Justin and Selena are happy with their alleged blossoming romance, Justin's ex Jennifer is reportedly "not happy about it." The source adds that Jen, who shares the same manager with Selena and Justin, is not just a friend to Selena, but also "a mentor."

Another source tells HollywoodLife.com, "Jennifer is upset over the dating rumors swirling around her ex and Selena. It hurts Jen to think that Justin would move on already."

"To think of him with anyone else, especially someone so young and that Jen has a personal relationship with like Selena, is painful for her," the source continues. "Jen doesn't want to think about it and definitely does not believe it."

"Jennifer is tired of hearing about all the women Justin may be dating since their split," adds the source of the "Friends" alum. "From Emma Watson to Selena, Jen is furious over every picture she sees of her ex with another pretty face out in New York. Jen won’t believe any of the rumors until she hears from Justin himself that he is involved in a new relationship."