Sienna Miller looked stunning in a simple white summer dress as she stepped out in west London on Thursday night for the Debute pop-up shop opening party. The actress, 44, put on a leggy display in the £250 Jazzy broderie mini dress from the latest collection, which she paired with black sandals and a Prada straw beach bag. She had a messy bun and stylish sunglasses as she sat soaking up the sun and chatting with guests. Sienna was joined by Rita Ora’s sister Elena, who wore a plunging black lace dress. She paired the racy number with white heels and a matching lace bag. Launched in October 2024, Debute is a London-based womenswear brand founded by sisters Jazzy De Lisser and Lola But. New mum Sienna Miller put on a leggy display in a white summer dress as she joined Elena Ora at a London pop up shop event on Thursday night The actress, 44, paired her summer ensemble with black sandals and a Prada straw beach bagTheir two day summer pop up in Notting Hill is taking place on Friday and Saturday and showcases the brand’s SS26 collection, Between Tides.The event marked Sienna’s second outing of the week after attended the Serpentine Gallery Summer Party on Tuesday. She made the slightly bizarre decision to wear a huge, fur-lined coat over a silk dress – despite scorching London temperatures reaching almost 40C (104F) this week. She styled it out however with strappy heels and a matching gold bag as she posed just six weeks after giving birth to her third child.Sienna welcomed her third child in May, her second with fiance Oli Green. They also had a daughter in January 2024.The actress also has a daughter, Marlowe, 13, from her relationship with ex-partner Tom Sturridge.In an interview with Hello!, Sienna’s sister, fashion designer Savannah, praised 29-year-old Oli’s beautiful proposal to Sienna, who just gave birth to her third child.Savannah said: ‘We are all so over the moon. It’s the happiest news, and it was beautiful, the whole thing. I can’t express how happy I am for her.’Rumours of Sienna’s engagement began last week when she stepped out with a new diamond ring on her wedding finger. Scooping her blonde locks off her face in a casual up do, she accessorised with stylish sunglasses as she sat soaking up the sun and chatting with guests Sienna welcomed her third child in May, her second with Oli Green. They also had a daughter in January 2024 Sienna was joined by Rita Ora’s sister Elena who wowed in a plunging black lace dress She paired the racy number with white heels and a matching lace bag The guests were seen chatting outside the summer boutique pop up shop Debute Elena beamed in snaps as she posed for pictures She made the slightly bizarre decision to wear a huge, fur-lined coat over a silk dress to the Serpentine party – despite London temperatures reaching almost 40C (104F) this weekShe showed off her bling on a trip to Barcelona, where she was seen leaving a party only a week after giving birth.It is the fourth time Sienna has become a fiancee, although she has never yet been married.Friends of the couple say former model Oli has long made known his desire to marry Sienna, despite being 15 years her junior.One said: ‘Oli and Sienna are so ridiculously in love, they’ve got a lovely family and have such a giggle together.’He knows what a catch Sienna is and wants to make her his wife. Hopefully it will be fourth time lucky and Sienna will make it to the aisle this time.’Onlookers in the Spanish port city told how the actress ‘couldn’t stop smiling.’Sienna is yet to reveal her third baby’s sex or name.