Jessica Biel on what makes her marriage to Justin Timberlake work: 'We believe in honesty, loyalty'

Jessica Biel and husband Justin Timberlake have plenty in common where it counts.

The stunning 35-year-old actress covers Marie Claire's August issue, in which she opens up about their enviable relationship. Biel says shared values and a strong work ethic is what keeps them together.

"We have similar values; we believe in loyalty, honesty," Biel tells the magazine. "We like to have fun. We like a lot of the same things. Also, in the business, we're all very career-oriented, and you have to be a little selfish. I understand that about my peers -- about being focused and driven -- and if you can find that and someone who shares the same values as you, it's like: Score!"

WATCH: EXCLUSIVE: Jessica Biel Opens Up About How She and Husband Justin Timberlake Inspire Each Other

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Biel and 36-year-old Timberlake are parents to their adorable son, 2-year-old Silas, and the actress admits life has definitely changed since becoming a mother.

"You think you're a selfless person, and then you realize you're not," she says. "These little people come around, and they require so much, and your schedule is really not your own, nor is it important anymore, and it's very clear that it's your life now revolving around this dude. I'm not that person who feels like, 'Oh, my whole life changes for my kid,' but it does."

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Still, the busy star is still making time for projects she's passionate about, including USA's The Sinner, a psychological thriller based on Petra Hammesfahr's best-selling novel. Biel plays Cora, a young American mother, who stabs a stranger to death while she's with her family at the beach. Biel says exploring her dark side for the role has been good for her.

"I have challenges standing up for myself sometimes," she explains. "Times when I don't trust my own voice. And that's the stuff I needed to bring out and explore to understand Cora."

"It's like a drug, like an adrenaline rush," she adds. "There's a real're exhausted, you are free; you feel a lot of different things. For me, it's like a rebirth. Like I'm a phoenix rising up out of the ashes."

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ET spoke to Biel at the Tribeca Film Festival, where she talked about her dark role in The Sinner, which premieres on Aug. 2 on USA.