Ken Jennings Fears Mayim Bialik's Return to 'Jeopardy!' Could Be the Final Nail in His Reign as Host: Report

Brainiac Mayim Bialik teased her Jeopardy comeback in a new promo video after sitting out as host during the writer's strike — and now sources say her return has game show rival Ken Jennings quaking, RadarOnline.com has learned.

The Big Bang Theory star, 47, took over as host of the popular trivia game show from January to May, when she left in solidarity for the WGA strike. Jennings, 49, took over as host in her absence.

According to the National Enquirer, Jennings is said to be "freaking out" now that Bialik is set to reclaim her hostess gig — and firing up the rivalry that was put on ice when she walked out to support Hollywood writers.

"A triumphant return was always her plan," an insider revealed to the outlet. "Ken's been less than popular on the set since she left and he's worried she'll wind up taking his place permanently."

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Former contestant Jennings became a fan favorite in 2004 when he notched a stunning 74 consecutive Jeopardy victories. But since signing-on as part-time host to replace late legend Alex Trebek, insiders reportedly claimed that Jeopardy's biggest-winning contestant has been branded a condescending jerk by the show's crew.

Now sources on the set say they believe his decision to cross picket lines made him less popular with folks who believe he did it in a bid to brown-nose producers into making him the show's only host!

"Ken got very cocky without Mayim there and demanded he be treated like a king," sources alleged. "He rubbed a lot of people the wrong way — including some of the decision makers!"

The insider added that because of Jennings' alleged behavior, "he's in a tough spot."

Since Trebek's passing, the longtime popular game show has struggled to captivate audiences amid its on-going host drama, which was said to make both Jennings and Bialik fear they'd be canned in favor of hot, young talent.

"Pat Sajak's departure and the way Vanna White's been treated serve as a stark reminder there's no room for complacency in this cutthroat game show world," an insider dished back in July. "Ken and Mayim are under no illusions about that!"

The source noted that the actress and former contestant both apparently came to the realization that a truce was needed in an attempt to salvage their part-time positions, even amid ongoing rumors that Bialik was vying to be top dog at the show.

"There's a serious possibility they'll both be booted in favor of some hotshot," the insider said of the part-time hosts playing nice to save their game show careers.