Sienna Miller is expanding her family with boyfriend Oli Green. Miller, 43, was all smiles as she debuted her baby bump at the British Fashion Awards on Monday, December 1, rocking a sheer white strapless Givenchy gown and styling her hair in loose waves. "@siennathing is pregnant!" the official Vogue Magazine Instagram account wrote on Monday. "The star revealed she is expecting her second child at 43 with partner Oli Green at the #BritishFashionAwards this evening, in a @givenchy dress and all." Miller became a mom when she welcomed her eldest daughter, Marlowe, with ex Tom Sturridge in 2012. The exes dated from 2011 to 2015 before she moved on with Green, whom she was first linked to in 2022. Two months after she was spotted with Green, Miller revealed that she froze her eggs when she turned 40 because of the "pressure" to add to her family. Sienna Miller Is Pregnant With Baby No. 2, Her 1st With BF Oli Green "Biology is incredibly cruel on women in that decade [of their 30s] - that's the headline, or it certainly was for me. Then I got to 40 and I froze some eggs," she told Elle UK at the time. "Having been really focused on the need to have another baby, I'm just like, if it happens, it happens. That kind of existential threat has dissipated." Later that year, Miller spoke about her plans to expand her family. Joe Maher/Getty Images for BFC "I'd invested what felt like the important years in something that was just a bucket with a hole in it of a person. I wasted time. And I felt like time was really my currency," she told British Vogue in November 2022. "There was a lot of anxiety. Relationships hadn't worked out - I imagined that I would be married with three kids, being a great mum." One year later, news of Miller's second pregnancy broke when she was spotted showing off her baby bump in a bikini while vacationing in Ibiza. In January 2024, Daily Mail confirmed that Miller gave birth to a baby girl, her first child with Green. The couple has yet to publicly reveal their daughter's name. Sienna Miller Gives Birth to Baby No. 2, Her 1st With Oli Green Since welcoming their first child, Miller has been candid about the pair's relationship. In June 2024, Miller told Harper's Bazaar that she "didn't expect to take it seriously" in the early days of their romance. "And then quite quickly, I fell in love," Miller said, recalling that she was surprised by Green's age when they met. "I wasn't like, 'I'm gonna get a younger boyfriend.' It was more, 'F***! Why are you young? That's so annoying.'" In Miller's eyes, her 14-year age gap with Green has actually been a positive part of their relationship. "There is a difference in the way that generation of men respect women," Miller shared. "It's specific to him, he is very wise and well-adjusted, but I do believe it's also that generation. They have grown up with a slightly more level playing field. I see it in his female friends as well as in the men."