Actress Emily Blunt's boyfriend has been exposed as an alleged love rat by a blonde bombshell who claims she has been dating him behind the Brit's back. Tiffany Bromley, 28, insists she has been dating Canadian singer Michael Buble on and off for the past decade. And she claims some of their encounters have taken place while he's been dating Blunt, the star of The Devil Wears Prada. Bromley tells U.S. tabloid the Globe, "Michael is a cheater and a rat. We've made mad, passionate love a couple of times since he and Emily have been together. The last time was August 17 in the apartment they share in Vancouver." And Bromley claims that sexy encounter was "an 11 out of 10" experience that ended with Buble allegedly suggesting they took a series of naked photographs and then took part in a threesome. She adds, "I told him, 'No way!' He said, 'Don't knock it till you've tried it. You don't know what you're missing.'" But the threesome didn't happen and they just made love through the night, surrounded by Blunt's belongings. The following morning Bromley woke before Buble, took cameraphone photos of him sleeping and then left wearing one of his designer shirts. She claims Buble called her later furious that she'd left with an item of his clothing - and that was the last time she heard from her ex.