“Extra” first broke the buzz of a Justin Timberlake and Jessica Biel couple alert.

Now, Justin’s first romance after saying adios to Cameron Diaz is the big story on the cover of the new Us Weekly.

The magazine’s Katrina Szish gave “Extra” the hot new details of how it all started.

“Things are definitely heating up between Jessica and Justin,” Szish dished. “Jessica and Justin first crossed paths in early December at the L.A. hotspot Social, and then about a month later she was spotted backstage at one of his concerts.”

But Us Weekly said, for now, this is the ultimate undercover romance.

“They are really trying to keep things quiet after a very public make out session at the Golden Globes; they were very, very low key at Sundance,” she said. “They spent most of their time holed up in his condo.”

Click on an image to view the Justin Timberlake or Jessica Biel photo gallery!