Gwen Stefani must have discovered the fountain of youth at the end of the ‘90s: She hasn’t really aged past her No Doubt days. On the newest edition of "Carpool Karaoke," the singer finally revealed one big reason why she looks so young at 46.

Her secret? She fell in love, and then she wrote a whole album about it.

"I’m writing music that’s about happiness and truth!” Stefani said during her passenger-seat interview with host James Corden. Credit goes to country singer Blake Shelton, who’s been her muse and her new beau since her split from Gavin Rossdale.

It wouldn’t be "Carpool Karaoke" without a few sing-alongs, and of course Corden and Stefani hit up “Don’t Speak.” She also spelled out the most confusing lyrics to her solo song “The Sweet Escape."

When Corden hit the four-person carpool lane, he rang up two of his best Hollywood pals to help out: George Clooney (who keeps aging beautifully) and Julia Roberts (who also doesn’t age) joined the carpool just in time for “Hollaback Girl” to come on.

It turns out Clooney has a very manly baritone, even when he’s singing Queen’s “We Are the Champions."