Sienna Miller, 42, flashes her midriff in a chic black crop top co-ord as she opens The Treasure House Fair – five months after giving birth to second child

Sienna Miller looked effortlessly chic in a black co-ord set as she opened The Treasure House Fair at the Royal Hospital in Chelsea, London, on Thursday.

The 42-year-old Hollywood star showed off a glimpse of her baby bump in a stylish puff-sleeved crop top and matching skirt.

The Burn star – who gave birth to her second child five months ago – looked radiant and showed off her natural look with barely there make-up.

Sienna added floral maxi pendant earrings that added a pop of color to her ensemble, beaming as she posed at the event and later took the stage for a speech.

The fair, which takes place from June 27 to July 2, brings together 70 leading galleries and covers more than 20 collecting categories in the fields of fine art, furniture, antiques and jewelry.

Sienna Miller, 42, looked effortlessly chic in a black co-ord set as she opened The Treasure House Fair at the Royal Hospital in Chelsea, London, on Thursday.

The Burn star looked radiant and showed off her natural look with barely there makeup

The Burn star looked radiant and showed off her natural look with barely there makeup

Earlier on Tuesday, Sienna appeared on Jimmy Kimmel Live! that was taken over by Martin Short, beginning Jimmy Kimmel’s summer hiatus as there will be a rotation of guest hosts filling his spot.

Martin was joined by his friend Steve Martin and the comedians greeted Sienna warmly before she hilariously explained that she had already met them.

She recalled, β€œIt’s funny that you say nice to meet you, we actually met. I had this horrible experience. Do you remember Dimitri in the Sunset Tower, the sweetest man, the greatest man in the world?

β€œI think he had the tactic of thinking there’s a somewhat famous person and two very famous people and I want them to meet.

‘So he came up to me and said, ‘Marty Short and Steve Martin want you’. And I clearly died a thousand deaths, you know icons!

‘So I come to your table and I’m beside myself and I say, “Hi” and I’m standing there… And you’re both like, who are you? You’re a crazy person!’

Sienna also talked about her new film Horizon: An American Epic: Chapter 1, directed, co-written, produced by and starring Kevin Costner.

The film is the first of four films chronicling a multifaceted, fifteen-year period of expansion and settlement of the American West before and after the Civil War.

The Hollywood star showed off a glimpse of her midriff in a stylish puff-sleeved crop top and matching skirt

The Hollywood star showed off a glimpse of her midriff in a stylish crop top with puffed sleeves and a matching skirt

Sienna added flower-shaped maxi pendant earrings that added a pop of color to her ensemble

Sienna added flower-shaped maxi pendant earrings that added a pop of color to her ensemble

The actress beamed as she posed for photos at the event

The actress beamed as she posed for photos at the event

Kevin plays pioneer Hayes Ellison in the new film, who treks through dangerous territory across the West in hopes of a new life.

While Sienna stars as Frances Kittredge in the historical epic, which will be released in two chapters on June 28 and August 16 this year.

They are the first two of four planned parts for the film series, which Kevin has been desperately trying to bring to life for more than 30 years.

The 69-year-old Dancing With Wolves star is said to have personally raised $50 million of Horizon’s $100 million budget.

Describing how she came to the project, Sienna told Martin and Steve: β€œI got this call from Kevin Costner, which was exciting enough because I’m a child of the nineties.

‘And I get four scripts on my desk – the desk breaks because they are incredibly dense and heavy. And we had a conversation and I’m so excited because he’s Kevin Costner and he’s a legend.

“And at the end he says, ‘Sienna, I have one question for you. Will you come west with me?’ I said I would go to Mars and back.”

Her TV interview comes after Sienna gushed about her ‘wise’ and ‘well-adjusted’ boyfriend Oli Green, saying his ‘generation of men’ has more respect for women.

The couple was first linked in February 2022 and welcomed a baby girl together five months ago.

She made rare comments about her relationship in an interview this month, praising 27-year-old Oli as “wise and well-adjusted” and saying his generation of men respects women more.

Sienna faced public humiliation in 2005 when her then-boyfriend Jude Law, now 51, confessed to cheating on her with his children’s nanny, Daisy Wright.

About Oli, she told Harpers Bazaar magazine: β€œI didn’t expect to take it seriously, and then I quickly fell in love.

“I wasn’t like, ‘I’m going to get a younger boyfriend.’ It was more, “F*ck! Why are you young? That’s so annoying.”

While appearing on Jimmy Kimmel Live!  Sienna also talked about her new film Horizon: An American Epic: Chapter 1, directed, co-written, produced by and starring Kevin Costner (pictured together last month)

While appearing on Jimmy Kimmel Live! Sienna also talked about her new film Horizon: An American Epic: Chapter 1, directed, co-written, produced by and starring Kevin Costner (pictured together last month)

The film is the first of four films that chronicle a multifaceted, 15-year period of expansion and settlement of the American West before and after the Civil War.

The film is the first of four films that chronicle a multifaceted, 15-year period of expansion and settlement of the American West before and after the Civil War.

Kevin plays pioneer Hayes Ellison in the new film, who treks through dangerous territory across the West in the hope of a new life, while Sienna stars as Frances Kittredge (pictured)

Kevin plays pioneer Hayes Ellison in the new film, who treks through dangerous territory across the West in the hope of a new life, while Sienna stars as Frances Kittredge (pictured)

Her TV interview comes after Sienna gushed about her 'wise' and 'well-adjusted' boyfriend Oli Green, saying his 'generation of men' have more respect for women (pictured last month)

Her TV interview comes after Sienna gushed about her ‘wise’ and ‘well-adjusted’ boyfriend Oli Green, saying his ‘generation of men’ have more respect for women (pictured last month)

‘There is a difference in the way the generation of men respects women. It’s specific to him, he’s very wise and well-adjusted, but I do believe it’s that generation too.

‘They grew up on a slightly more level playing field. I see it with his girlfriends as well as with the men.’

As well as the five-month-old baby she shares with Oli, she has daughter Marlowe, 11, with her ex-partner Tom Sturridge.