Jessica Biel visits Justin Timberlake at Sundance!

Justin Timberlake isn't wasting his time getting back in the saddle after his split from Cameron Diaz in December. He's been spending a lot of time lately with gal who is also on the rebound: Jessica Biel. Though Biel had recently been dating Yankees shortstop Derek Jeter, it looks like she's moved on entirely to Timberlake.

Jessica and Justin were first linked earlier this month when she attended his concert in San Diego with some friends. But things really heated up between the pair at the Golden Globes afterparties. They were spotted flirting at a number of different gatherings, but really made a splash at the Creative Artists Agency event at Sunset Towers, reports Us Weekly. That's where Justin's ex got involved. When Cameron saw Justin with Jessica, "she just lost it," a spy told Us. "She came up and started yelling at Jessica." Another onlooker said, "First she started saying all these nasty things to him about Jessica like, 'What is she? Your new f**king girlfriend? Look at her!' And then she insinuated things about other guys that Jessica has been with."

Diaz's tirade hasn't stopped Biel and Timberlake from pursuing their romance, however. Sources for Perez Hilton say that the former "7th Heaven" star traveled out to the Sundance film festival On Thursday to be with her new man. An insider told Perez, "Jessica was picked up in her chauffer-driven Volkswagen Touareg car and instantly went to visit Timberlake when she got into Park City."

Don't feel too sorry for Cameron and Derek, though. While she's been linked to pro-surfer Kelly Slater since the break up with Timberlake, he has been sowing his oats as well. Last weekend Jeter was "flirting madly" with Bring It On star, Gabrielle Union, a source for Page Six reports. Derek and Gabrielle were at Atlantis in the Bahamas for the Michael Jordan Golf Tournament where they did some "dirty dancing" to the song "Put It in Your Mouth" by Akinyle. They were seen leaving together later, though Union's rep said, "They are friends, but they did not hook up."