Hollywood power couple Sienna Miller and Lucas Zwirner have allegedly parted ways. The couple had been seeing each other for more than a year.

The news about Sienna Miller and Lucas Zwirner's breakup was first reported by Page Six claiming that the report was confirmed to them by "sources exclusively." As per the publication, the sources revealed that the split was apparently initiated by a 38-year-old actress.

"The Loudest Voice" heroine reportedly called things off for reasons that remain unclear. The couple was engaged for months, however, they never commented on the reports.

It is said that the 29-year-old editor, who is also the son of art gallery and publishing house owner David Zwirner, had proposed Miller for marriage in January. The couple was at a portrait studio at the Sundance Film Festival that month for the premiere of her latest movie "Wander Darkly." During this outing, she was spotted wearing what "looked like an engagement ring." And she was apparently seen it wearing "as recently as July." Nevertheless, the couple never confirmed the news of engagement or breakup.

Miller and Zwirner got engaged after a year of romance. As per the outlet, the couple had some trouble before they got engaged. Nevertheless, they were spotted together running errands, until last month. Apart from this, they were also photographed at Ellie Goulding and Casper Jopling's marriage last year and pre-Met Gala party.

While the news of their separation is yet to be confirmed, a source reveals that Miller "would bounce back."

Previously, in June, a source told Us Weekly that the couple was "already planning their nuptials."

"They're so in love," a source shared at the time. "Her daughter [Marlowe] has a nice and close relationship with Lucas too. They're excited for this new chapter," the source added.

Sienna Miller
Sienna Miller recalled her embarrassing first meeting with Mark Wahlberg on tonight's Graham Norton (16 June) Rich Fury/Getty Images

Prior to Zwirner, Miller was engaged to actor Tom Sturridge with whom she shares an eight-year-old daughter Marlowe Ottoline Layng Sturridge. Before Sturridge, Miller was in a long-term relationship and engaged to Jude Law.