The British actress is heavily pregnant with her first baby – thought to be due in July – and her friends and family can hardly wait to meet the new arrival.
Blossoming Sienna was the main attraction when she stepped out with some of her girls at a book launch in London this week.
Stepmother Kelly Hoppen could barely keep her hands off Sienna’s burgeoning baby bump as she fussed over the mum-to-be.
Also enjoying an afternoon out with the pregnant star were her older sister Savannah and Kelly’s daughter Natasha Corrett.
The ladies had teamed up to support Natasha, a gourmet chef specialising in organic food, at the unveiling of her healthy lifestyle guide.
With weeks to go before she becomes a mum, the blonde beauty has undoubtedly been relying on the support and expertise of her sister, with whom she is very close.
Savannah is herself a mother of three children, one of them baby daughter Bali joined her mum on the girls' day out.
It was at the start of the year that reports first emerged that Sienna was expecting a baby with 26-year-old English actor Tom Sturridge, best known for his role in The Boat That Rocked.
She confirmed the happy news in an interview with British Vogue in March, saying that her pregnancy was "progressing nicely" and that she was in her second trimester.
Sienna and Tom, who are thought to be engaged, have been dating for over a year following the actress’ split from Jude Law in January 2011.
And earlier this month, they were spotted enjoying a romantic 'babymoon' together in Italy looking very much in love.
Ahead of the holiday, Sienna, 30 spoke about her excitement, saying: "I’m going on holiday soon, which will be lovely; it’s a pre-baby, last hurrah trip.
"I'm in the mood for lying on a beach, reading a lot of books and a bit of culture," she told InStyle.
"I like being able to walk into an old town and find good local food."
French Open flirting for tennis fan Sienna Miller and actor Tom Sturridge