Sienna Miller baby is reportedly a girl named Marlow. Awww.

Details of Sienna Miller's baby have been kept firmly under wraps since she reportedly gave birth at the weekend.

Sienna Miller, baby, girlSienna Miller has reportedly had a little girl named Marlow. Copyright [Rex]

But according to sources in America the actress and fiance Tom Sturridge have had a little GIRL.

And American gossip site E! Online are claiming that the couple have named their first baby MARLOW.

US Weekly initially broke the news at the weekend that Sienna Miller had given birth in London.

But neither the birth, gender or name have been officially confirmed by the couple yet.

Sienna Miller, babySienna Miller and Tom Sturridge have had their first child. Copyright [Wenn]

British star Sienna was similarly tight-lipped throughout her pregnancy and it took the actress's step-mother Kelly Hoppen to confirm the news.

Rumours she was expecting first surfaced in January this year.

Sienna did comment on looking forward to the next chapter in her life saying : "I'm in my second trimester, so I'm I-can-talk-about-it pregnant. It's a nice start to a new decade."

And she told British Vogue recently: "Even though I'm under strict instructions not to say anything... I'm feeling fine."

The 30-year-old star was spotted throughout her pregnancy out and about showing off her bump in a range of gorgeous maternity wear.

The couple have been together for over a year.