Jon Hamm sings with Beck during a secret show at hip downtown bar

The hottest party of New York Fashion Week had nothing to do with fashion.

Downtown cool kids and rock royalty got a side of Hamm during an exclusive, secret performance by rocker Beck at hip bar, the Mulberry, this weekend.

“Jon Hamm, will you help us play a song? Jon Hamm, are you here?,” Beck called out from a makeshift area set up at the small basement bar following his show at Madison Square Garden on Saturday.

The “Mad Men” star then joined the “Loser” singer and went ham, belting out the entirety of the Cars 1978 hit, “Just What I Needed,” in front of music heavy hitters like the Strokes’ Julian Casablanca and their manager Ryan Gentles, the Black Keys’ Patrick Carney, the Moldy Peaches’ Adam Green and Brit rockers, the Arctic Monkeys.

Jon Hamm, Beck — Jon Hamm sang the Cars “Just What I Needed,” with Beck during a secret show and party following the rockers Madison Square Garden show.

“He really added some Hamm-bience,” joked one guests, as many chattered about how well Don Draper can sing.

The “Virgin Suicides” director Sofia Coppola, “Scream Queen” Emma Roberts, Sarah Hyland, creative director Thomas Hayo, singer Charlotte Kemp Muhl, Celine’s Peter Utz, Alicia Solo, and Beck’s mom, Warhol Superstar Bibbe Hansen were also in the crowd for the late night show that started after 1a.m.

“1901” band Phoenix, who also played Madison Square Garden as part of the Summer Odyssey tour, were at the party, which offered up a menu inspired by both artist’s songs, like a “Listztomania,” and “Devils Haircut.”

Jon Hamm — The crowd included members of the Strokes, Phoenix, and the Arctic Monkeys.

Phoenix was also going to play the subterranean space, but disappointingly wound up leaving before Beck finished his set.

Hamm was at the bash with his new wife Anna Osceola, with whom he tied the knot in June 2023 in Big Sur, California.

“The Mulberry is NYC’s Viper Room,” Beck was heard saying, referring to the famed Sunset Strip spot owned by Johnny Depp that was an epicenter for the rock scene before River Phoenix died from a drug overdose on the street outside in 1994.