Sienna Miller says her newborn daughter Marlowe is ''so cute''.

The 30-year-old actress and her fiance Tom Sturridge, 26, welcomed their first child into the world last month and Sienna is smitten.

Speaking to Us Weekly recently, Sienna, who is keeping the baby close by at all times, gushed: ''She's so cute... She's screaming upstairs. My brain doesn't work.''

Although news of Sienna's pregnancy broke earlier this year, the 'G.I. Joe: Rise of Cobra' star was initially very reluctant to talk about it.

The blonde beauty admitted she did not want to share details of the pregnancy because she didn't want anything to ruin her attempts to keep her private life out of the public domain.

In March, she said: ''I'm in my second trimester, so I'm I-can-talk-about-it pregnant, 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.''

Sienna started dating 'The Boat That Rocked' actor Tom - who is friends with Robert Pattinson - just a few months after she split from fiance Jude Law for a second time in February 2011.