VIDEO: Letterman Grills Jessica Biel About Boy Friend Justin Timberlake

Jessica Biel, the girlfriend of Justin Timberlake, told David Letterman Wednesday night how the sexy pair's romance developed -- and it had nothing to do with his junk in a box.

The fit actress -- who plays a stripper in her latest film, Powder Blue -- said that her courtship from with the former 'N Sync frontman was sparked by a mutual friend, and grew as the comely couple burned up the phone lines.

When a leering Letterman prodded her about the content of the the chats, Biel laughed, and playfully slapped the talk show host's arm, insisting they were "PG."