The emotional moment came in Monday's episode when Trebek read Dhruv Gaur's final answer.
Instead of writing a correct response, Gaur wrote "We love you, Alex!" He substituted a heart in place of the word love.
Trebek's voice cracked slightly as he thanked Gaur, telling him, "That's very kind."
Gaur was eliminated in the semifinals for the Tournament of Champions. He tweeted that Trebek had just "shared with us that he was reenteering treatment" and "we were all hurting for him so badly."
Trebek announced in September he had resumed chemotherapy.
The Final Jeopardy clue had sought the title of a groundbreaking 1890 expose of poverty in New York City slums.
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