She has been dating Foxcatcher director Bennett Miller for more than a year, after they met on the set of the 2014 movie.
And Sienna Miller sparked rumours of a proposal on Wednesday night, after flashing a sizeable diamond ring on her engagement finger while stepping out in London.
The 35-year-old actress, who was previously engaged to actor Tom Sturridge, looked chic in flame-print co-ords as she left a performance of Cat On A Hot Tin Roof.
Rumour has it: Sienna Miller sparked rumours of a proposal from boyfriend Bennett Miller on Wednesday night, after flashing a sizeable diamond ring on her engagement finger while stepping out in London
What’s that then? The 35-year-old actress flashed a dazzling round diamond ring on her left hand
The blonde beauty looked typically chic in the silky printed pyjama shirt and loose matching palazzo pants.
Opting for comfort, the Alfie star completed her ensemble with a pair of white flatform trainers and accessorised with a black and white woven leather tote.
Smiling coyly, the British beauty seemed oblivious to the attention her dazzling ring commanded as she stepped out without her beau Bennett.
It seems to be the first public outing for the significant piece of jewellery, as Sienna wasn’t spotted wearing the ring at a fashion party last week.
Smitten: She has been dating Foxcatcher director Bennett Miller for more than a year, after they met on the set of the 2014 movie
Looking good: The blonde beauty looked typically chic in the silky printed pyjama shirt and loose matching palazzo pants
Loving life: Smiling coyly, the British beauty seemed oblivious to the attention her dazzling ring commanded as she stepped out without her beau Bennett
MailOnline has contacted a representative for Sienna for comment.
Sienna met Bennett on the set of drama Foxcatcher, with sources confirming to MailOnline in June that they are ‘happily’ still together.
The pair keep their romance under wraps, and were last seen in public at the US Open last September.
Sienna and Bennett, who share the same surname and whose December birthdays are just two days apart, were alsp seen attending Wimbeldon twice together in July that year.
Something to smile about? Sienna appeared to be in great spirits as she left the theatre
Radiant: Styling her glossy blonde hair in a simple middle parting, she wore minimal make-up to showcase her striking features
They had reportedly been dating in secret for months in 2016, with a source telling Us Weekly that Bennett accompanied the BAFTA-nominated star to a Met Gala afterparty last May.
In 2015, Sienna spoke to Vogue about working with the director as she said: ‘He opened the door to a world of filmmakers I didn’t have access to before.
‘Directors speak to each other… Everybody calls the last director you worked with, so it being Bennett Miller was a hugely beneficial thing.’
Cute couple: Sienna met Bennett on the set of drama Foxcatcher, with sources confirming to MailOnline in June that they are ‘happily’ still together
New addition? It seems to be the first public outing for the significant piece of jewellery, as Sienna wasn’t spotted wearing the ring at a fashion party last week
Sienna separated from her former fiancé Tom Sturridge and has previously dated Jude Law. In August 2014, Bennett dated Ashley Olsen.
Meanwhile, in July the blonde beauty dismissed claims she is dating Brad Pitt , 53, after reports surfaced claiming they were ‘exploring a casual summer romance’ – in what would have been his first romance since splitting with Angelina Jolie , 42.
Despite the reports, sources told MailOnline the star is happily dating Bennett, with insiders stating: ‘Sienna’s finding it all very funny with friends have been texting her about Brienna laughing’.
Former flames: Sienna and actor Tom met in 2011 and became engaged the following year – shortly before she gave birth to daughter Marlowe Ottoline Layng Sturridge. They split in 2015
It was claimed that the Hollywood stars had been trying to keep their dates a secret, according to new reports, but their cover was seemingly blown when they were seen looking very intimate in a Glastonbury VIP area.
Despite the reports, sources told MailOnline: ‘She’s happily with Bennett and has no idea where these rumours keep coming from.
‘They’re just not true. Brad’s a great friend but nothing more. They were hanging out at the Rabbit Hole at Glastonbury but they were with a big group.’
In the past: When the star first soared to prominence with her role in Alfie, she soon fell for her co-star Jude, who she became engaged to in 2004
It’s over: He went on to cheat on her with his children’s nanny in 2005 before they split the following year