Kate Moss believes Sienna Miller will break Rhys Ifans' heart.
The supermodel - who had a blazing row with Sienna at a wedding last month when she accused the "Factory Girl" actress of stealing her style and friends - is said to have warned the 39-year-old Welsh actor, who is her close friend, that Sienna is bad news.
A designer friend of Sienna's told Britain's Daily Express newspaper, "Kate isn't happy. Rhys was her main male friend in her close-knit group. She isn't keen on Sienna. There is definite tension between them."
"Sienna was fuming after Kate gave Rhys a talking to when she heard the relationship was getting serious. Kate doesn't think it will last and doesn't want Rhys getting hurt."
Despite Kate's misgivings, the pair - who have constantly denied they are a couple, despite being pictured frequently together and even seen kissing in public - are said to be so in love they are even considering getting married.
The source continued, "Sienna is probably the happiest I've ever seen her. She and Rhys are perfect together. They are having such a great time, I wouldn't be surprised if they got engaged."
Sienna's ex-lover Jude Law - who she dated on/off for three years - has given the relationship his seal of approval.
Last week, it was claimed Rhys had already proposed to Sienna, 25, five times, but the screen beauty had so far spurned his marriage offer.