After delivering some adorable one-liners and a particularly raunchy Donald Trump joke, Corden came storming out, half-dressed, and demanding an answer to why the pop star was trying to steal his thunder.
"What? You just figured you'd come out and do my monologue?" Corden asked angrily. "No! That's like me coming out and trying to sing one of your songs! I mean I could. Brilliantly."
Gaga explained that, after giving Corden a ride to work earlier in the day, she had hoped to just hang out and sit in on the show.
At first the host resisted, but after Gaga prompted some cheering from the audience, Corden offered her the chance to sit in with band leader Reggie Watts for the whole show and occasionally sing some tracks off her new album, Joanne.
Gaga then brought her wild style and serious road rage to "Carpool Karaoke,"
driving with through the streets of Los Angeles while enthusiastically singing some of her new singles and some of her biggest hits with the excited host.
In a "Carpool Karaoke"
first, Corden let Gaga take the wheel to give him a ride while they sang. He did, however, strap on his safety helmet, as Gaga famously didn't learn to drive until recently and only got her driver's license in July.
Even with precautions like a safety helmet, the English comedian couldn't handle more than a few blocks and one nervously-sung Gaga hit until he demanded she pull over so he could get back behind the wheel.
From her red lace Alexander McQueen ensemble at the 2009 MTV Video Music Awards to her infamous meat dress from the 2010 VMAs to her white Francesco Scognamiglio Dress (complete with towering white wig) from the 2010 Brit Awards, Corden has never looked better dressing up like one of his "Carpool" guests (except for maybe when he rocked Britney Spears' schoolgirl getup
from her "…Baby One More Time" music video).
Easily the best moment came when Corden started picking scraps of cold-cuts off his meat dress to eat, just to show Gaga how gross the outfit really was, even when she wore it.
As the fun, energetic ride neared its end, Corden and Gaga wrapped up with her new single "Million Reasons," and the 30-year-old singer delivered what may have been the most powerful performance in "Carpool Karaoke" history.
Gaga's vocal range and impassioned delivery actually seemed to catch Corden off-guard as he occasionally forgot to even sing along and instead, just gazed at her in awe.