Sienna Miller and Lucas Zwirner have split.

The 'American Sniper' star has reportedly ended her romance with the gallery owner, just months after it was reported they were engaged.

The New York Post's Page Six column is reporting that it was Sienna's idea to end the relationship with the art dealer.

Meanwhile, it was previously revealed Sienna ''can't wait'' to marry Lucas.

An insider said at the time: ''Sienna can't wait to make him her husband. They are both looking forward to the wedding. Lucas loves how family-oriented Sienna is, and she loves that Lucas is youthful and fun.''

Sienna - who has eight-year-old daughter Marlowe with her ex-partner Tom Sturridge - and Lucas, 29, were first rumoured to be engaged in February, but the couple never confirmed the speculation.

A source said at the time: ''They're so in love. Her daughter has a nice and close relationship with Lucas too. They're excited for this new chapter.

Sienna had previously said she ''loves'' Lucas and she would be open to marrying him in the near future.

She gushed: ''It is love. It's nice and settled and happy. Yes, I would love to have more children. I would love a daughter as well. I think I would be open to getting married, yes. He's not an actor! He's not famous!''

Back in 2019, Sienna admitted she wants to have more children and wishes she had her daughter when she was younger.

Asked what it was like playing a grandmother in her 30s in her new movie, Sienna admitted: ''I loved it. I'm up for anything. It didn't even cross my mind. What makes me laugh is that Sky Ferreira still calls me mum, which is funny. She's older than she plays. No, I loved it. Also, that exists. I'm kind of envious. I wish I'd had my daughter younger, and I could have grandchildren now. I'd like more children at my age now, too. There's something to be said for that dynamic. I was 30 when I had [my daughter]. It's a horrible facing of mortality. So, I'm all for young babies.''