Laura Prepon Shows Off Her Growing Baby Belly on the Red Carpet with Fiancé Ben Foster

Laura Prepon is ready to pop!

On Wednesday night, the Orange Is the New Black actress stepped out with her fiancé Ben Foster to attend the premiere of her new film The Hero at the Whitby Hotel in New York City.

Prepon, 37, who is expecting her first child with Foster, 36, was all smiles as she rested her hand on her growing baby belly, wearing a polka-dotted off-the-shoulder Envie de Fraise top and a bold red lip.

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The low-key duo — who have known each other for almost two decades — have largely kept their relationship under the radar, though sources confirmed to PEOPLE in October that the two were engaged. (Even Prepon’s close friend and former That ’70s Show costar Ashton Kutcher was out of the loop about it!)

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In January, PEOPLE confirmed the news of Prepon’s pregnancy, just one day after the couple attended the Creative Coalition’s annual Spotlight Awards at the Kia Supper Suite during the Sundance Film Festival.

“Ben seemed really protective and kept very close to Laura the entire night,” an onlooker told PEOPLE. “He was holding onto her arm as they walked in and kept by her side during the dinner.”