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(TMZ) - Jan Hooks, who worked alongside some of the biggest "Saturday Night Live" stars ... died Thursday ... TMZ has learned. She was 57.

TMZ reports she passed away this morning in New York City. Sources tell TMZ Jan had been battling a serious illness.

Jan was part of the 'SNL' cast from 1986-91 ... the same time as Chris Farley, Mike Myers, Phil Hartman, Dana Carvey and Dennis Miller ... and was most famous for being one half of the Sweeney Sisters with Nora Dunn, as well as impressions of Sinead O'Connor and Hillary Clinton.

She most recently played a part on "30 Rock."

Right after 'SNL', Jan joined the cast of "Designing Women." She also had a famous role in Pee Wee's Big Adventure.

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