NEW YORK -- Will Ferrell finally triumphed over his arch enemy: Conan O'Brien's beard.

Ferrell culminated a weeks-long lead-up to Monday's episode of "Conan" by shaving the late-night host's beard. A giddy and determined Ferrell guest-starred on the program, promoted as the "Beardpocalypse."

While guzzling Barbicide, Ferrell trimmed O'Brien with clippers, which he named "Excalibeard." He had promised O'Brien that the razor "sleeps for no one."

Ferrell did a haphazard job of it, but the shave was finished off-camera. It was the first time O'Brien gave up the beard he grew after NBC jettisoned him from the "Tonight Show."

Seeing O'Brien's fresh-faced mug again, Ferrell turned remorseful, saying he had made a "terrible mistake."