Josh Dallas has clearly cast a spell on his Once Upon a Time costar Ginnifer Goodwin.

Weeks after Us Weekly first reported the two had been secretly dating since last fall, Dallas, 33, and Goodwin, 30, made their first joint red carpet appearance at the "My Valentine" music video premiere party, hosted by Paul and Stella McCartney, in West Hollywood Friday.

"They were cute, but not overtly affectionate," an eyewitness tells Us. "They were standing shoulder to shoulder though and talking low and leaning in to each other smiling."

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Another observer spotted the costars slow dancing to The Ink Spots' "I Don't Want to Set the World on Fire" later that evening. "It was a very cute moment, as the couple seemed to lose track of the fact that they were not the only people in the room."

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The event brought out some of Hollywood's biggest stars, including Gwyneth Paltrow and Chris Martin, Miranda Kerr and Orlando Bloom, Kristen Stewart, Gwen Stefani, Zooey Deschanel, Jane Fonda, Pamela Anderson and a pregnant Reese Witherspoon.

Goodwin and Dallas' relationship didn't surprise their costars. At the opening night of Billy Elliot in Hollywood Thursday, Raphael Sbarge -- who plays Jiminy Cricket/Archie Hopper on the ABC fantasy series -- told Us "they're so lovely" together.

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"There's such genuine affection, which you can see on screen," Sbarge gushed. "You can see how they just interact with each other. It's genuine."

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