Laura Prepon Engaged to Ben Foster -- See the Flawless Ring!

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Laura Prepon and Ben Foster have taken their relationship to the next level.

Prepon, 36, and Foster, 35, are engaged, a source confirms to ET. The couple attended The New York City premiere of The Girl on the Train on Tuesday night, when the Orange Is the New Black actress showed off her sparkly new diamond ring on that finger.

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ET confirmed that Prepon and Foster were an item in July, when they were spotted out multiple times together in New York City. Foster last dated House of Cards actress Robin Wright, but they broke off their engagement twice, for the final time in August 2015. As for Prepon, she broke up with former Greek star Scott Michael Foster in 2013 after five years together.

ET spoke with Prepon on Tuesday at her big premiere, when she stunned in a lacy blue Naeem Khan dress. Prepon said the highly anticipated film stays true to the beloved Paula Hawkins bestseller it's adapted from.

"We're actually pretty accurate to the book, as where Orange [Is the New Black], we really kind of splinter off into, you know, different worlds," she told ET. "I mean, it's amazing. It's a great thing to be a part of. It was on the [New York Times Best Sellers] list for an insane amount of time, and it's a beautiful book. And I think that we do that justice with the movie."

Although she didn't speak out about her engagement, she did gush about her loved ones.

"All my friends are so supportive and amazing," she said about their excitement to see The Girl on the Train finally hit the big screen. "They're supportive of anything I do."

WATCH: EXCLUSIVE: Laura Prepon Reveals Her Secret to Losing Weight for Good

Interestingly enough, Prepon's engagement isn't the only happy news on the Orange Is the New Black set. Writer Lauren Morelli and actress Samira Wiley announced their own engagement on Tuesday.

Watch the video below to see Prepon react to her first ET interview when she was just 18 years old, and the advice she gave herself that has stuck with her to this day.

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