Heartthrob Ryan Gosling may still technically be dating his girlfriend of three years Eva Mendes, but the hunky actor may have made a big move which indicates his still smoldering affections for one particular ex-girlfriend -- his The Notebook co-star Rachel McAdams.

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The 33-year-old actor reportedly proved he still has lingering feelings for his ex after reports first began surfacing earlier in June that she had begun dating another famous Hollywood heartthrob -- Jake Gyllenhaal.

"The moment he heard Rachel was getting close to Jake Gyllenhaal, he called Kayleen [McAdams' sister] up to find out the truth," a source told OK! Magazine June 26.

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McAdams and her Southpaw co-star first sparked rumors they were dating after they were spotted out together twice in one week earlier this month. The Daily News reports they were spotted having a dinner together at Meat and Potatoes Restaurant in Pittsburgh June 3, but they were also seen catching the Miguel Cotto vs. Sergio Martinez fight at Madison Square Garden in New York on June 7.

The two were reportedly just watching the fight in order to research their roles for their upcoming film, but sources have said that Gyllenhaal does find himself attracted to McAdams, and thinks she's the 'whole package' when it comes to the kind of woman he wants to date.

"There is no denying the electric chemistry between Jake and Rachel. The attraction was instant. From the moment they started working together, Jake and Rachel just connected intellectually and emotionally," a source said at the time.

"For Jake, Rachel is the complete package. She's incredibly smart and well versed in arts, politics and culture, but she's not a show-off. Of course, it helps that she's gorgeous," the source added.

If Gosling is reportedly still pining for his onetime 'great love of his life,' it could spell massive trouble for his relationship with Mendes, which has been weathering constant rumors of a split for six months. The couple have reportedly been on/off for much of their relationship, and Mendes' conspicuous absence at her beau's directorial debut at the Cannes Film Festival in May has made many wonder if the couple have quietly split again.

"There's been trouble in paradise for quite some time," the source told OK!, adding that both have jealous streaks, and Mendes is still extremely insecure over her beau's history with his ex.

"She has always been intimidated by Ryan's history with Rachel, and her insecurities could soon be realized," the source added.