And what's even better, he makes sure not to steal the spotlight from the Total Recall star.
J.T. avoided the red carpet this afternoon at Variety's annual Power of Women luncheon at the Beverly Wilshire Hotel, where Biel was given Tiffany & Co's Luminary Award for her work with Charity: Water.
Instead, he snuck in through the back.
And Timberlake, 31, beamed as Jennifer Garner, 40, gushed over his fiancé, 30, while presenting her with the award. He let out a big whopping holler when Garner revealed, "Her brand of humor is bawdy, much bawdier than you might even imagine."
And she's quite helpful, too.
"I know Jessica to be a true girl's girl," Garner said. "She's the kind of girl who will check that you don't have lipstick on your teeth and your Spanx aren't sticking out. She has got your back."
In thanking Garner, Ms. Biel said, "You're one of those magical women who can be everywhere and do everything and make it all look so easy.
"There's a fine line between admiring someone and creepily wanting to actually be them," she continued. "And I feel like I'm constantly walking that line with you."
And could the two women be trying to put together a big-screen adaptation of a classic 1970s sitcom?
After Garner said Biel "will always be the Shirley to my Laverne," Biel agreed, but then she added, "Even if we never make that movie."
Biel didn't mention J.T. during her remarks, but told E! News on the carpet that she is no "bridezilla" when it comes to planning their wedding. "I'm just pretty much cool as a cucumber in general in my life," she said. "So no, I'm cool."