Sienna Miller’s renaissance! Actress, 42, wows fans as she showcases her incredible post-partum figure just four months on from daughter’s birth after crediting yoga and Marmite as the secret to her age-defying looks

Sienna Miller stunned fans when she showed off her incredible figure in a £3,900 dress at a star-studded birthday party just four months after the birth of her second child.

The fashionista, 42, and her boyfriend Oli Green, 27, welcomed their first child together, a girl, in January. Sienna also has a daughter Marlowe, 10.

Sienna joined make-up artist Charlotte Tilbury and models Poppy Delevingne and Cora Corre at Lady Lola Bute’s 25th birthday party, held at the family’s Mount Stuart House on the Isle of Bute.

Sienna stood out from the crowd in a £3,900 silk mesh dress by Annie Doble of Annie’s Ibiza.

It featured hand-beaded crystals in the shape of a spider web and a backless design, while the sheer nature of the dress highlighted her lithe figure.

She paired the look with a nude bodysuit and a tan, as she had just returned from a family holiday in Croatia.

The designer also produced a custom-made outfit in a 1920s Egyptian fabric for Lady Lola.

While Lola and Annie shared photos from the bash on Instagram, Sienna firmly cemented her fashion icon status as she posed for a photo with Annie and Camille Charriere.

The actress has barely aged a day since starring in Layer Cake and Alfie more than twenty years ago.

Sienna previously gave insight into and opened up about her health and fitness regimen Fashion: ‘I do yoga three times a week…more because I’m just looking for some equanimity. It’s very easy to feel exhausted by these schedules and time zones.”

The New York-based actress said at the time that she was not a big fan of the spin class SoulCycle.

She said: ‘Sometimes I cringe a little at the motivational aspect of it, but that’s only because I’m English and we’re not used to saying, “You see your dream! Go and get it”‘.

“Cooking is a focus for me,” Sienna shared, “but I wouldn’t say healthy… I’m more of a home cook: roasts, some Asian food, pastas and sauces and soups. In terms of, say, chia seeds and any grains, no. I’m like, ‘Fried eggs and Marmite toast.’

The party saw hundreds of guests fly to the remote Scottish island for the party of aristocrat Lady Lola, daughter of the late John Crichton-Stuart, 7th Marquess of Bute and fashion designer Serena Bute.

Guests partied for a weekend, dancing in the 19th-century neo-Gothic dining room and sleeping in large bedrooms that looked straight out of a fantasy novel.

Princess Olympia of Greece and Lady Mary Charteris danced with members of the Guinness family, who took down Iron Bru during a festival-themed party during the day before switching to more sophisticated dirty martinis with their black tie attire in the evening.

Rare snaps from inside the Mount Stuart House were also shared, including a grand staircase, an ornate ceiling pattern and even the slightly old-fashioned toilet.

The seat of the Marquess of Bute, a title now held by Lola’s brother, the manor has been held since 1157.

However, the current house, which is grade A, was built in the late 1870s and replaced an earlier house.

This weekend, however, the house got a major makeover, with giant inflatable mushrooms and teepee as part of the party setup.

After partying all night, guests also enjoyed their time on the island, taking to the sea and gawking along the beach.

In keeping with the Scottish theme, Lola also enjoyed a bagpipe band and drummers in kilts.

The party was organized by Lola’s half-sister, Jazzy De Lisser.

Jazzy is the daughter of Serena and her first husband Robert De Lisser.

Despite her party girl antics, Lola is down to earth and has sought help for “unhealthy coping mechanisms” following the suicide of her boyfriend Kai Schachter and the accidental overdose of her best friend Ila Scheckter.

After Kai’s death, she founded the charity Eternity to raise awareness of suicide, addiction and mental health, which she said helped her “heal and cope with grief in a healthy way.”

Her father, John Crichton-Stuart, spent much of his time on his eponymous Scottish island at his family home, Mount Stuart, and had been chairman of the board of directors of the Mount Stuart Trust since 2005.

The 7th Marquess, once ranked 616th in the Rich List, was also a Formula 1 driver in 1986 when he teamed up with Ayrton Senna and raced under the name Johnny Dumfries.