Justin Timberlake: 'Sexyback' on 'Fallon' with Allison Williams!

Justin Timberlake joins The Ragtime Gals to sing a barbershop quartet version of his 2006 hit single “SexyBack” during an appearance on Late Night with Jimmy Fallon on Tuesday (March 12) in New York City.

Later in the show, the 32-year-old entertainer continued his week long appearances with a performance of his song “Mirrors” off his new album The 20/20 Experience.

PHOTOS: Check out the latest pics of Justin Timberlake

Allison Williams was also spotted appearing on the show and took the time to sign autographs and pose for pics afterwards.

Earlier in the day, Allison held onto an umbrella while stepping into NBC Studios for an appearance on New York Live…

FYI: Allison is wearing a Narciso Rodriguez dress, Jimmy Choo shoes, Nam Cho earrings, and a Jill Alberts ring.