The article cites the reason for the split as Ifans' jealousy. The floppy-haired Welshman had allegedly grown suspicious over the possibility that Sienna was rekindling her love with former flame Matthew Rhys.
Having to communicate long-distance, the couple had grown apart in recent weeks and Miller reportedly broke the news to Ifans over the phone. According to the source Sienna found Rhys looking through text messages on Sienna's phone.
"She went bananas and Rhys said he was looking for what he called 'incriminating evidence.' He has been giving her a hard time lately, questioning her commitment to him and the time she puts into the relationship," the insider dished.
Sienna claims that she and her ex are simply close friends, however time will tell whether or not that's true.