The "Bury a Friend" songstress jumped in the passenger seat of Corden's SUV for a new, surprisingly inspirational installment in the beloved Late Late Show segment -- while a longer, more in-depth cut was posted to YouTube shortly after.
The segment began like many others, with Eilish and Corden singing along to her hit single "Bad Guy," and sharing fun banter.
Eilish reflected on freaking out when she saw Justin Bieber in the crowd during Ariana Grande's performance at Coachella earlier this year. Corden also busted out a ukulele, on which Eilish performed the first song she ever wrote, when she was only 7 years old.
The simple but beautiful tune, called "What a Wonderful Life," actually moved Corden, who called the tune "glorious."
The entire segment felt remarkably more personal than many other "Carpool Karaoke" bits, and Eilish seemed genuinely excited to sing her own tunes. She even got a little emotional while singing along to "Ocean Eyes," which she wrote and first sang when she was 13.
"I haven't listened to that in so long," Eilish shared. "That song is the reason that I have the life I have."
Eilish also explained how her and her brother Finneas, the co-creator of her album, made the whole thing as a passion project in their small home.
"Luckily, with us, me and my brother, we made the whole album, and the EP, in his little bedroom in our house," she reflected. "No booth, no studio, just the bedroom."
This inspired Corden and Eilish to take a special trip to the singer's home, and she showed Corden Finneas' bedroom, where they recorded the entire album.
"Before we made any songs together, Finneas said [something], kind of as a joke, but we were talking about making music together, and he goes, 'I'm gonna make you the biggest pop star in the world.' And we just laughed," Eilish recalled while laying in her brother's bed.
Corden spent most of his time marveling at being at the site of musical genius -- and getting terrified by Eilish's pet tarantula -- before he got to meet Eilish's mom, Maggie Baird.
"People are like, 'How does it feel that she's singing at Radio City?' Like, it blew my mind when she sang at the Hi Hat. It blew my mind when I sat here and heard Billie and Finneas play a song. It's never not been mind-blowing," Baird shared. "So it's almost been like four years of, 'Oh my God.'"
The sweet and loving bond actually brought Corden to tears, and the English host asked to be a part of the family. For anyone of Eilish's millions of fans, this "Carpool Karaoke" broke the mold in a really rewarding way.