When Justin Timberlake and Cameron Diaz announced their split earlier this week, most of us assumed it was because Cameron, nine years Justin's senior, is ready to settle down and have kids, while Justin, 25, still wants to party. But it turns out the real culprit may be blonde vixen Scarlett Johansson.

Johansson was cast to play the "Britney" role in JT's new video, "What Goes Around Comes Around," about Britney's cheating on him. Scarlett's decision to accept the role seemed strange coming from someone who spends her days doing Woody Allen films. But Scarlett may have been thinking about more than her career when she said yes. According to an Us Weekly source, “Scarlett has always liked Justin. They’ve always had a flirtation – that’s why Cameron was threatened by her.”

Justin's decision to cast Scarlett pushed Cameron over the edge: "She could not believe he went behind her back to put her in the video. Cameron was very jealous of Scarlett.” Us Weekly's source claims that JT and ScarJo "definitely" hooked up after filming the video.

Britain's News of the World chimed in with this tidbit about the Alpha Dog premiere after-party in L.A.: "She walked in keeping her head down. When she met Justin they looked very close and chatted away for ages. There were other people trying to speak to Justin but he kept his attention on her for around an hour. They looked very intimate."

If it's any comfort to those of you mourning the JT/Cam split, I'll note that the fact that Cameron Diaz got her ass flat-out dumped for a girl over a decade younger will probably give Britney Spears something to drink to tonight. Not that she'll need a reason.

The Evil Beet

Celebrity gossip with an evil twist.