Sienna Miller cuts a radiant figure in stylish all-white ensemble as she arrives at Jimmy Kimmel Live! to promote Horizon: An American Saga

Sienna Miller looked effortlessly stylish on Monday, as she arrived at Jimmy Kimmel Live! in Los Angeles to promote her new Western film Horizon: An American Epic.

The actress, 42, cut a cheerful figure as she smiled and waved to waiting fans on her way into the studio. 

Displaying her impeccable fashion sense, she sported a pair of high-waisted white trousers and a casual cream tank top.

Sienna added a pair of white trainers and a brown leather belt to cinch her in at her tiny waist, while carrying her essentials in straw tote bag.

She completed her look with a dainty gold chain necklace, a slew of matching bracelets and hoop earrings.

Sienna Miller looked effortlessly stylish on Monday, as she arrived at Jimmy Kimmel Live! in Los Angeles to promote her new Western film Horizon: An American Epic

The actress, 42, cut a cheerful figure as she smiled and waved to waiting fans on her way into the studio

Displaying her impeccable fashion sense, she sported a pair of high-waisted white trousers and a casual cream tank top

She pinned her blonde hair back with several strands left down and curled to frame her face, while hiding her eyes behind a pair of purple tinted sunglasses.

The mother-of-two looked in high spirits ahead of her TV appearance and was spotted handing out autographs.

Later Sienna was spotted leaving the studios, having undergone a wardrobe change into another chic white ensemble. 

The Anatomy of a Scandal star looked summer ready in a cream maxi dress with lace and ruffle detailing for the Horizon: An American Epic premiere.

Still toting her straw bag, she swapped her comfy trainers for a pair of black slouchy knee-high boot, with a quirky half-painted wooden heel.

Sienna also added a chunky gold choker and a host of beaded bracelets, while her hair was style in soft waves and she wore a light palette of minimal makeup.

Later in the evening she appeared on the late night show, which was taken over by Martin Short, kicking off Jimmy Kimmel's summer hiatus where there will be a rotation of guest hosts filling his spot.

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

Sienna added a pair of white trainers and a brown leather belt to cinch her in at her tiny waist, while carrying her essentials in straw tote bag

She completed her look with a dainty gold chain necklace, a slew of matching bracelets and hoop earrings

 She pinned her blonde hair back with several strands left down and curled to frame her face, while hiding her eyes behind a pair of purple tinted sunglasses

The mother-of-two looked in high spirits ahead of her TV appearance and was spotted handing out autographs

She recalled: 'It's funny that you say lovely to meet you, we've actually met. I had this horrible experience. Do you remember Dimitri at the Sunset Tower, the sweetest man, the greatest man in the world?

'I think he had a 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 to me you". And I died a thousand deaths obviously, you know icons! 

'So I come up to your table and I'm beside myself and I say, "Hi" and I stand there... And you were both like, who are you? You crazy person!'

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

The film is the first of four chronicling a multi-faceted, 15-year span of pre-and post-Civil War expansion and settlement of the American West. 

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

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

Later Sienna was spotted leaving the studios, having undergone a wardrobe change into another chic white ensemble

The Anatomy of a Scandal star looked summer ready in a cream maxi dress with lace and ruffle detailing for the Horizon: An American Epic premiere

. Still toting her straw bag, she swapped her comfy trainers for a pair of black slouchy knee-high boot, with a quirky half-painted wooden heel

Sienna also added a chunky gold choker and a host of beaded bracelets, while her hair was style in soft waves and she wore a light palette of minimal makeup

Later in the evening she appeared on the late night show, which was taken over by Martin Short, kicking off Jimmy Kimmel's summer hiatus where there will be a rotation of guest hosts filling his spot

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

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

The Dancing With Wolves star is thought to have personally raised up to $50 million of Horizon's $100 million budget.

Describing how she came onboard the project, Sienna told Martin and Steve: 'I got this call from Kevin Costner, which exciting enough because I am a child of the 90s. 

'And I get four scripts on my desk - the desk breaks because they're incredibly dense and heavy. And we had this chat and I'm so excited because he's Kevin Costner and he's a legend.

'And at the end of it he says, "Sienna I have one question for you. Will you go West with me?" I said I would go to Mars and back.'

Her TV interview comes after Sienna gushed over her 'wise' and 'well-adjusted' boyfriend Oli Green and said his 'generation of men' are more respectful to women.

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

Making rare comments about her fiercely private relationship in an interview this month, she lauded Oli, 27, as being 'wise and well-adjusted' and said his generation of men respect women more.

Sienna also spoke about her new film Horizon: An American Epic: Chapter 1 directed, co-written and produced by, as well as starring Kevin Costner (pictured together last month) 

The film is the first of four chronicling a multi-faceted, 15-year span of pre-and post-Civil War expansion and settlement of the American West

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

Sienna famously 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.

Speaking about Oli to Harpers Bazaar magazine, she said: 'I didn't expect to take it seriously and then quite quickly, I fell in love. 

'I wasn't like, "I'm gonna get a younger boyfriend." It was more, "F*ck! Why are you young? That's so annoying."

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

'They have grown up with a slightly more level playing field. I see it in his female friends as well as in the men.'

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

Sienna opened up about family life during a candid interview with The Guardian, following a 'rough baby night' with her youngest daughter.

She explained that the 10-year age gap between her daughters is, 'actually quite useful because one is tiny and portable, and the other is becoming increasingly independent.'

Speaking about Marlowe, who walked the Cannes red carpet with her mother last month, Sienna said: 'She's so stylish and very critical.'

'She's like a young Anna Wintour in her total disdain for some of the things I wear. In New York she thought I was mortifying. She wished I would brush my hair.'

Her TV interview comes after Sienna gushed over her 'wise' and 'well-adjusted' boyfriend Oli Green and said his 'generation of men' are more respectful to women (pictured last month)

Sienna famously 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 (seen in 2004)  

As well as the five-month old she shares with Oli, she has daughter Marlowe, 11, with her ex partner Tom Sturridge (pictured with Marlowe and Oli last month)