Hollywood's Unlikely Heartthrob, Michael Sheen: What Gives?

Michael Sheen isn't your traditional Hollywood hunk, but, make no mistake, he's a hot commodity.

The "Masters of Sex" star is dating comedian Sarah Silverman, according to the new Us Weekly. He arrived at his 45th birthday party earlier this month with Silverman, whose most famous ex is Jimmy Kimmel, and they shared a smoldering makeout session at Soho House in West Hollywood soon after.

The curly-haired Welshman isn't exactly an obvious heartthrob. He's not snapping shirtless selfies all day (hello, Justin Bieber!) or flexing his muscles on the cover of Men's Health. He's better known for his impressive resume (in addition to his Golden Globe nod for "Masters," he's received three BAFTA nominations for his movie roles, including "The Queen"), but the bachelor's dating history is impressive as well.

Sheen's longest relationship was with Kate Beckinsale, with whom he has a 14-year-old daughter, Lily. They were together for almost a decade, and remained close friends after she went on to marry their "Underworld" director, Len Wiseman, soon after their split. When the brunette bombshell relocated to Los Angeles, Sheen also moved in order to be closer to them. In fact, Beckinsale and Wiseman were among the guests at Sheen's birthday party and hang out at other Hollywood events, like recent Golden Globes afterparties.

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In addition to his romance with Beckinsale, the Hollywood import also was in a two-year relationship with Rachel McAdams, whom he got to know while co-starring in "Midnight in Paris." And she wasn't the only smitten beauty. Right after his split from Beckinsale, he dated English ballet dancer Lorraine Stewart for about five years. Other women he's been linked to include his "Masters" co-star and on-screen wife Caitlin FitzGerald (last summer) and TV host Carrie Keagan, who was with him at the New York premiere of the Showtime series last fall.

So what is it about the guy — who seems to fall into the adorkable category with his unassuming presence on the red carpet and sometimes unruly curls — that is so irresistible?

Other than the charmer's talent, comedic chops (how great was he opposite Tina Fey in "30 Rock"?), and, of course, the cute accent, Beckinsale called him a "magical person" to Cinema.com back when they were dating, noting that he always did romantic things for her. He favorite thing about him? "He's protective of the people he loves, so I'm very glad I'm one of those."

Watch Sheen excitedly chat about his on-screen collaberations with Tina Fey:

After their split — which she described as "elegant," explaining that it was less dramatic than it seemed — she called him "a very supportive, brilliant man with whom I spent nearly 10 years," she said in another interview. "Even though people might not want to believe it, Michael and I are still friends and he's still a big part of Lily's life and she couldn't have a better father. That's what's important to me rather than all the other speculation."

She continued, "I love him dearly – I would miss him dreadfully if he wasn't in my life. He is one of the most thoughtful, principled people and Lily is so lucky to have him as a dad. I've been very lucky to have two marvelous men in Len and Michael, they've got no awkward feelings about parenting Lily and working things out. I'm very proud of both of them that they haven't let any potential awkwardness or strangeness affect our little family."

For McAdams, she became smitten with his "British sense of humor," she told the U.K.'s Telegraph. "Michael is a very funny person." And their relationship started as a friendly one, which she said helped give them a solid foundation. "Michael and I didn't get together while we were filming 'Midnight in Paris,' which I feel strongly about not doing when I'm working. We became quite good friends, which I think is a great way to start."

He was also willing to make an effort to see her often. "Michael and I never spend more than three weeks apart," she told Stella magazine, "but you have to be quite adaptable in this business whether you are in a relationship or not.

And celebrities aren't the only ones to fall for him. His on-screen talent seems to be what wins him fans.

"He's just awesome on Masters Of Sex! Such an amazing actor!" Tatjana wrote on Twitter. "Love his facial expressions & body language."

Though a possible dealbreaker for his real-life leading ladies could be that he doesn't seem committed to the idea of settling down. There were rumors that when he was with McAdams, she was ready for the next step and he wasn't. That seemed to be the case with Beckinsale before they ended up going their own ways.

"When I was doing the interviews for 'Pearl Harbor,' everybody kept asking the same thing," she told Scottish Daily, referring to why she hadn't married Sheen after eight years together. "And I was too embarrassed to admit I really didn't know why Michael hasn't got round to proposing to me yet. So I would make up stories like 'when Lily's old enough to be our flower girl, we'll get married.' But the truth is that Michael hasn't asked me to be his wife yet. I actually asked Michael outright, 'Why aren't we married yet?' I couldn't believe it when he said, 'Because every time I was going to ask you, you did something annoying.' So maybe if I can hold off being annoying for a while, then he'll finally ask me. But I should add that Michael is brilliant and wonderful."

Brilliant, wonderful, and … the object of affection for many.