The 46-year-old singer joined James Corden for the Carpool Karaoke segment of his show on Wednesday night's episode (04May16). As he spoke to Gwen, James admitted his wife had told him to ask her how she maintains her ageless "Benjamin Button" type appearance.

And in response, Gwen said it's her new relationship with Blake, who she started dating in November (15), that she believes is responsible for her flawless look.

"What happened was, my life blew up. After that I kind of started falling in love, and then I wrote a whole record about that. So this is like, it’s almost like, that’s what the facelift is, I think," Gwen laughed.

"I’m writing about happiness and truth."

The carpool took a tense turn when James pulled into the HOV4 lane, meaning he needed four people in the vehicle to be able to use that lane. So he decided to call on one of his Hollywood pals to give him a hand - George Clooney.

Getting in the car, George told James "you're a pain in the a*s", before the host told him he needed another person. At that point George decided to enlist the help of his Money Monster co-star Julia Roberts.

Once all four stars were safely in the car, James moved on, and the group listened to Gwen's hit Hollaback Girl. George and Julia appeared to know all the lyrics to the track, with the 54-year-old actor particularly seeming to enjoy the line: "This s**t is bananas. B.A.N.A.N.A.S."

Asked what he thought a Hollaback Girl was, George replied: "I know what Hollaback Girl means, it means if some guys on a construction site shout at a girl, she’s not going to shout back, she’s not going to Hollaback. Am I close?"

But Gwen refused to confirm what she was inspired by when she penned the track, cryptically saying: "It’s your interpretation of the song.

"The real inspiration behind that song I will never say. All I will say is ‘I won’."