Saturday Night Live - Season 42"Late Late Show" episode.

When it came time for Corden to come out an deliver his opening monologue, Lady Gaga took the stage instead. Stealing the host's thunder and calling herself "Lady Haha," she started in on the usual topical jokes. Yet, she only got through a few before a pants-less Corden ran onstage to reclaim his show.

The two staged a faux argument over her supposed hijacking, but they quickly reached a compromise that viewers' loved: Gaga got to stay as part of the band. Naturally, she didn't have to hide away -- she performed one of the singles from her new album, "Joanne," and interacted with guests.
Another highlight of the show was Lady Gaga's "Carpool Karaoke" segment. Between that and her unexpected appearance, the audience got a healthy dose of Gaga.
"The Late Late Show with James Corden" airs weeknights at 12:37 a.m. ET on CBS.