Sienna Miller in Primrose Hill, London on May 24, 2012. Credit: BAR/

When it came time to name her new baby girl, Sienna Miller stayed true to her U.K. roots.

The British actress, who gave birth to her and fiance Tom Sturridge's first child in London over the weekend, named her daughter Marlow, sources tell E! News.

Marlow is a unisex moniker of Old English origin; it means "driftwood," or "lake leavings" (referring to the area remaining after a lake has been drained), and was first used to refer to a region near Buckinghamshire, England.

Us Weekly first broke the news Sunday that Miller, 30, had welcomed her and Sturridge's bundle of joy. Throughout her pregnancy, the private actress stayed relatively mum on her and Sturridge's baby joy -- though she did open up to British Vogue in April about how things were going so far.

"Even though I'm under strict instructions not to say anything as it would completely defeat the point of everything I've tried to achieve in the last eight years, I'm feeling fine," Miller shared. "It's all progressing nicely and it's very exciting."