Sienna and her fiancé Tom Sturridge have reportedly named their little girl Marlow.
According to E! news, Sienna, 30, and Tom, 26, welcomed Marlow in London over the weekend, although the couple are yet to confirm the news themselves.
Sienna is notoriously private, and rarely spoke about her pregnancy, telling Vogue she was 'under strict instructions not to talk about it', so we're not expecting a big welcome-to-the-world OK! Magazine photo shoot any time soon... but we'll keep you posted.
Marlow. What do you think?