Sienna Miller Single Again?

Sienna Miller and Rhys Ifans will soon split up, according to friends.

The couple are said to be at the lowest point of their relationship and Sienna, 26, is said to be growing tired of 39-year-old Rhys, who she got engaged to in March.

A friend of the couple told Grazia magazine: "It's awful but everyone who knows them can just see it coming a mile off. Rhys seems madly in love with her still, but everyone is speculating Sienna has grown out of the relationship."

"It's almost painful to see them together because they've gone from being the perfect couple to him looking as if he's struggling to keep her attention. It's so sad."

The pair's troubles are said to stem from their hectic work schedules - Sienna has been busy shooting 'The Edge of Love' with Keira Knightley and 'G.I. Joe' with Channing Tatum, while Rhys has been busy working in the U.K.

Another friend told Closer magazine: "Sienna promised to spend a week with Rhys. He arranged his filming schedule, but at the last minute she canceled her trip, saying she had to work. Rhys hit the roof when he called her and found out she was partying in Los Angeles."

Rhys is also unhappy Sienna has been spending time with several Hollywood heartthrobs including Jared Leto and Sean Penn and her ex-boyfriend Matthew Rhys, who stars alongside her in 'The Edge of Love'.