Multiplatinum artist Kid Rock slammed television icon Oprah Winfrey on Saturday and called her a "fraud" after Winfrey endorsed the Pennsylvania Senate campaign of Democrat John Fetterman over his Republican opponent, Dr. Mehmet Oz, whom Winfrey has known and worked with for decades.

"Oprah helped Dr. Oz with his career," Kid Rock tweeted Saturday in a post that was retweeted over 10,000 times. "I assume because she vetted him and found him to be a wonderful person. Now she is against him. Oprah is a fraud. -Kid Rock."

Winfrey, a Democrat, announced on Thursday that she is supporting Fetterman’s Senate campaign despite her long relationship with Oz.

Oz first came to prominence as a health expert on "The Oprah Winfrey Show" before he got his own talk show in 2009, which was produced by Winfrey's company Harpo. His show ended in January. 

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Oprah Winfrey and Kid Rock

(L) Oprah Winfrey (R) Kid Rock (Getty Images)

"I’ll tell you all this, if I lived in Pennsylvania, I would have already cast my vote for John Fetterman for many reasons," Winfrey said during a virtual conversation with community leaders. 

Fetterman’s campaign said Winfrey’s support for the Democrat over Oz "speaks volumes." 

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Kid Rock performing on stage

Kid Rock performs at the Indianapolis Motor Speedway. (Photo by Michael Hickey/Getty Images)

"Oprah is widely regarded as the person who helped launch Dr. Oz’s career, and knows him well," the campaign said.

Kid Rock, born Robert Ritchie, has been a vocal critic of Winfrey’s in the past, including an on-stage rant at his honky-tonk in downtown Nashville, where he told the crowd "f*** Oprah Winfrey" and "f*** Joy Behar."

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"A drunk man’s words are a sober man’s thoughts, I own what I said," Kid Rock told Fox News’ Tucker Carlson on an episode of Tucker Carlson Originals on Fox Nation in June.

Representatives for Winfrey did not immediately respond to a request for comment from Fox News Digital.

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oprah winfrey

Oprah Winfrey speaks onstage during Oprah's SuperSoul Conversations at PlayStation Theater in New York City. (Bryan Bedder/Getty Images for THR)

"Doctor Oz loves Oprah and respects the fact that they have different politics," Rachel Tripp, senior communications adviser for the Oz campaign, told Fox News Digital in an emailed statement. "He believes we need more balance and less extremism in Washington."

Oz and Fetterman are currently locked in a tight Senate race in the Keystone State that a recent poll shows Oz leads by a margin of 1 percentage point.

The hotly contested Senate race could ultimately decide which party will control the Senate after Tuesday's midterm election.

Fox News’ Brie Stimson contributed to this report