Sienna Miller and Lucas Zwirner split

Sienna Miller and Lucas Zwirner have split up, sources exclusively told Page Six. There had recently been buzz in the art world and Hollywood that the couple — who were reportedly engaged — had called things off. A source told us that Miller broke off the relationship with Zwirner, who is nine years her junior, …

Sienna Miller and Lucas Zwirner have split up, sources exclusively told Page Six.

There had recently been buzz in the art world and Hollywood that the couple — who were reportedly engaged — had called things off. A source told us that Miller broke off the relationship with Zwirner, who is nine years her junior, though it’s unclear why.

Reps for Miller and for Zwirner’s gallery, in New York and London, did not respond to multiple calls and e-mails seeking comment on Monday.

Zwirner reportedly popped the question back in January. At a portrait studio at the Sundance Film Festival that month, where the actress debuted her latest film, “Wander Darkly,” co-starring Diego Luna, Miller was photographed sporting what looked like an engagement ring. Various paparazzi pics captured her wearing the ring as recently as July.

But the very private pair never publicly confirmed the engagement after a year of dating.

Miller, 38, has been engaged twice before: to Jude Law and actor Tom Sturridge, with whom she remains friendly and shares a daughter. She’s also been romantically linked to indie director Bennett Miller and actors Balthazar Getty, Josh Hartnett and Rhys Ifans.

Zwirner, 29, is the scion of his father’s powerhouse art gallery, David Zwirner, and he oversees its publishing house.

Sources said that the relationship between Miller and Zwirner had previously hit a rough patch before they purportedly got engaged.

They were most recently photographed together last month, running errands.

During their courtship, New York party people had clocked Miller and Zwirner around town when they were clearly deeply smitten. They also attended the starry wedding of Ellie Goulding and Caspar Jopling together last year, as well as a pre-Met Gala event.

But a source said that if they’ve parted ways for good, Miller would bounce back, adding, “She is awesome.”